Idle Stumble

[Allan R]

Q: On my 98 (1995 3800 series 2 non turbo) it just recently started dropping rpms while stopped in drive to around 650. Normally it would be around 690-700. Occasionally it will drop to around 620 and the car will shudder, but then it picks back up again. Is this a problem with the Mass air flow? Or is there some way to adjust the idle of the engine. The car has 146000 miles, but starts great and still gets great mileage city and highway. Any suggestions?

[bcracing]

Sounds like the IAC (Idle Air Control) solenoid may be either getting weak or is carboned up. It is a stepper motor, what it basically does is create a calculated vacumm leak in the throttle body which adjusted the idle speed. You can remove it and clean the end of it, and the passage in the throttle body, that may take care of it.

[70 cutlass s]

You may have vacuum leak need to check your vacuum lines. Is the service engine light on. If not may need tuneup if you don't have vacuum leak.

[Allan R]

Originally Posted by bcracing

Sounds like the IAC (Idle Air Control) solenoid may be either getting weak or is carboned up. It is a stepper motor, what it basically does is create a calculated vacumm leak in the throttle body which adjusted the idle speed. You can remove it and clean the end of it, and the passage in the throttle body, that may take care of it.

This 98 is EFI, not throttle body. Does it still have an IAC? The car gets a fair bit of highway, so it shouldn't have a lot of carbon buildup, but that's why I was wondering about the MAF sensor. According to what I've read, it can go wonky over time and create some performance issues. Note: I'm not a mechanic or electrician but I know how to work with tools and can do most basic and interediate work to the car. I like being hands on with my Olds. Its almost like the car knows that we share a relationship and gives back a lot for the effort being put into its longevity. This car probably is in better running condition after 14 years than most cars on the road with less than 3 years of service. I'm not the original owner so I don't know the previous history or have any mtce records b4 I bought it. Since I've owned it though, I have been almost anal about making sure this car is cared for properly, including doing body rust repairs, suspension, brakes, mechanical, exhaust, electrical, body integrity etc. It's one of the last 98 models built and I love the car. I don't want to end up stranded though by something that may be a routine mtce item. Do you know if MAF cleaning is part of the routine mtce cycle on a 3800 and what the intervals are? I'm not sure right now even where to look for the darn thing.

Originally Posted by 70 cutlass s

You may have vacuum leak need to check your vacuum lines. Is the service engine light on. If not may need tuneup if you don't have vacuum leak.

No, the SE light is not on. There's no vacuum lines to check on the 3800, and tuneup is basically just changing the spark plugs (which were changed only 35,000 miles ago. They should be ok for at least 60,000 according to GM spec). The car starts instantly, and runs exceptionally well during driving, has great top end power and still gets around 20mpg city and 37 mpg highway - if you drive economically. If you want to put your foot into it, it'll still go like a scared bunny.

[70 cutlass s]

There are vacuum lines they are plastic but they use rubber ends they do dry rot and cause vacuum leaks. If a MAF sensor goes bad this is what happens you start your engine up the engine idles up to 2500 rpm for about 30 seconds and dies. It does have an idle control motor its on the side of the throttle body I doubt if that's your problem. Here something else for you check battery cable ends clean them up. I have had the same problem with 3800 that's were I with battery cable ends works 99% of the time. The two hot cables going to a single hot post has to be cleaned often.

[dan2286]

I had a similar problem when I had my 00 Grand Prix with the same engine. Sometimes the idle would fluctuate and would sometimes start bucking while driving. When sitting at lights with the car in gear, the rpms would rise and sometimes would stall out. It rarely threw a code and when it did, it would be a misfire code. Eventually it started throwing a maf sensor code. Replaced that and the problem went away.

It did start with the fluctuating rpms at idle, then after awhile it started bucking while driving. Maybe that is something to look out for.

[Allan R]

Originally Posted by 70 cutlass s

There are vacuum lines they are plastic but they use rubber ends they do dry rot and cause vacuum leaks. If a MAF sensor goes bad this is what happens you start your engine up the engine idles up to 2500 rpm for about 30 seconds and dies. It does have an idle control motor its on the side of the throttle body I doubt if that's your problem. Here something else for you check battery cable ends clean them up. I have had the same problem with 3800 that's were I with battery cable ends works 99% of the time. The two hot cables going to a single hot post has to be cleaned often.

Ok, good tips. When my car starts it goes to about 1250 rpm and stays constant until 2 of the light bars on the digital cluster come on. Then it gradually lowers rpms until it reaches around 800. Once it goes into drive, it drops to around 700. I do keep the engine compartment clean and check the battery / terminals and connections regularly. Each terminal gets a dose of "no corrode" in the spring and fall. But, I'll try giving the connections and posts another wire brush and tightening to see if it helps. Come to think of it, this battery is 5 years old now. Maybe I should load test it to see if it's getting weak. Thx

Originally Posted by dan2286

I had a similar problem when I had my 00 Grand Prix with the same engine. Sometimes the idle would fluctuate and would sometimes start bucking while driving. When sitting at lights with the car in gear, the rpms would rise and sometimes would stall out. It rarely threw a code and when it did, it would be a misfire code. Eventually it started throwing a maf sensor code. Replaced that and the problem went away.

It did start with the fluctuating rpms at idle, then after awhile it started bucking while driving. Maybe that is something to look out for.

So far, the only thing I've noticed is the stumbling rpms while stopped at lights and in drive. It's even more noticeable when the def is on (because that pull the AC into play) and sometimes the rpms will momentarily stumble down to 620 or so. So far the driving part is really smooth and reliable. There is a little "lag" at shift points between 1st, 2nd and 3rd under heavier acceleration but the shift into overdrive is seamless. Did you get this too?

[Allan R]

Originally Posted by dan2286

I had a similar problem when I had my 00 Grand Prix with the same engine. Sometimes the idle would fluctuate and would sometimes start bucking while driving. When sitting at lights with the car in gear, the rpms would rise and sometimes would stall out. It rarely threw a code and when it did, it would be a misfire code. Eventually it started throwing a maf sensor code. Replaced that and the problem went away.

It did start with the fluctuating rpms at idle, then after awhile it started bucking while driving. Maybe that is something to look out for.

Hey, I just noticed you're in OH. I used to live down in Dayton back in 77- 78. (actually, I lived in a hotel - La Quinta, if I remember right it was just off I 75, while I was working for a computer company and flying back and forth a lot. But who cares, they footed the bill. Even paid for a rental except for personal mileage. I had to log that). North Ridgeville is nothin a cruise up a couple of interstates wouldn't cure!! Do they still drive like maniacs on I 90?

[70 cutlass s]

My 96 Pontiac loved batteries. I had to change them about every 3.5 years. Had new cables and I always did keep them clean. But it would act just like what you explained. Some times cleaning would fix it, but about every 3.5 year would have to change battery.

[dan2286]

Originally Posted by Allan R

Hey, I just noticed you're in OH. I used to live down in Dayton back in 77- 78. (actually, I lived in a hotel - La Quinta, if I remember right it was just off I 75, while I was working for a computer company and flying back and forth a lot. But who cares, they footed the bill. Even paid for a rental except for personal mileage. I had to log that). North Ridgeville is nothin a cruise up a couple of interstates wouldn't cure!! Do they still drive like maniacs on I 90?

To answer the last question about the shifting, no. The shifting was always fine on the car.

I consider most drivers in Northeast Ohio idiots They seem to think the fast lane is for doing the speed limit, don't know what blind spots are, and they seem to think they are the only one on the road. Don't even get me started about when snow comes

[Allan R]

Originally Posted by dan2286

To answer the last question about the shifting, no. The shifting was always fine on the car.

I consider most drivers in Northeast Ohio idiots They seem to think the fast lane is for doing the speed limit, don't know what blind spots are, and they seem to think they are the only one on the road. Don't even get me started about when snow comes

So, in a nutshell...nuthins changed. I also feel your pain. What I remember about OH winters was that no one adjusted to it very well. Either traffic was crawling (unnecessarily most of the time) or it was go like hell and hope for the best. It seems to be universal even here in Alberta. I'm glad I don't live in Vancouver. The gas and brake pedals only have 2 positions - full on or full off!

[bcracing]

Well I just got done working on my sons 97 GP 3800, his was doing the samething, The IAC had already been replaced, so wasn't that, turned out to be the MAF sensor. Replaced that and it idles like brand new. But his did throw a service engine soon light.

[dan2286]

I really don't think many things go wrong with those engines. I seem to hear about the maf sensor a lot, not to mention the intake manifold gaskets, and I have had some ignition problems. I still think that is one of the most bullet proof engines that gm has made.

[70 cutlass s]

I also like the 3800 I've owned a few and had to replace a couple one had the rod hanging side of the block. That what happens when right feet is a little heavy. The MAF does go bad it either has a rough idle or you start it up engine idles up than dies that it. If it has a rough idle they make a cleaner for MAF just take it out clean it put it back in.
On the 95 and up the heater bypass tube will leak after time coolant eat at the plastic tube. Most of the time when you change it the end brakes off so you have to take the intake off to get the broke piece out. Most of the ignition problems go back to the ground cable most people change out a lot of parts just find out it the ground cable. One problem they do with the ignition switch is a spring on the side does get weak. That's were the cable from the shifter button goes to the switch. What will happen is go turn off the car the key will not turn to lock pos. and the steering will not lock either. The problem that Allan is having is another problem the 3800 have it's simple in gear the idle drops just a little than back to normal it's either battery needs to be replaced or battery cable that needs to be cleaned or replaced. He said that his is 5 years old. That about the max one last in a car mainly one with a 3800.

[Allan R]

Originally Posted by bcracing

Well I just got done working on my sons 97 GP 3800, his was doing the samething, The IAC had already been replaced, so wasn't that, turned out to be the MAF sensor. Replaced that and it idles like brand new. But his did throw a service engine soon light.

The MAF should be in the same place on his GP I think. Where is it? I know it has to be after the air cleaner box. Also, where is the IAF sensor? I'll have a look later today. When you clean the MAF, do you just spray it down with electrical cleaner and let it dry? I've heard some suggestions that I could use brake cleaner too. What's your opinion? Thx.

Originally Posted by 70 cutlass s

I also like the 3800 I've owned a few and had to replace a couple one had the rod hanging side of the block. That what happens when right feet is a little heavy. The MAF does go bad it either has a rough idle or you start it up engine idles up than dies that it. If it has a rough idle they make a cleaner for MAF just take it out clean it put it back in.
On the 95 and up the heater bypass tube will leak after time coolant eat at the plastic tube. Most of the time when you change it the end brakes off so you have to take the intake off to get the broke piece out. Most of the ignition problems go back to the ground cable most people change out a lot of parts just find out it the ground cable. One problem they do with the ignition switch is a spring on the side does get weak. That's were the cable from the shifter button goes to the switch. What will happen is go turn off the car the key will not turn to lock pos. and the steering will not lock either. The problem that Allan is having is another problem the 3800 have it's simple in gear the idle drops just a little than back to normal it's either battery needs to be replaced or battery cable that needs to be cleaned or replaced. He said that his is 5 years old. That about the max one last in a car mainly one with a 3800.

Yup, had to replace the heater bypass tube on mine too. But I only found out about that because it was leaking out the top of the intake manifold and needed replacing. And sure as heck, that little plastic tube broke and it was not all that easy to fish out the broken piece. I'm going to try the MAF cleaning (see above bcracing) b4 I have to go out and buy a new battery. (I just pulled my service records and the battery is actually only 2yrs and 11 mo old - so it should be still good. It is 875 CCA and has a 3 yr full replacement, 9 yr prorated warranty).

[meoff]

I have a 1990 olds 98 touring sedan with 3.8 and the wife loves it!we've had it for over 10 years and is pushing 300kanytime I have had probs with the idle circuit as you are describing I used the G/M top engine cleaner.with engine idleing you spray it into the intake before the MAF and let it kill the engine and then pull the piping that connects the throttle plate to the filter box.then give the throttle butterfly a good spray and wipng with a rag and another another good spraying.reassemble and should be good to go and if not at least you know the upper end is clean

[Olds64]

I was thinking it might be the IAC motor as well. This was a common place for carbon to build up on the early to mid 90s cars. Ford had a similar problem, they just called their's an Idle Air Bypass. It is SUPER easy to remove the throttle body and clean the back of the throttle plate and the IAC motor. I think the gasket for the IAC and throttle body is about $8.00 at Auto Zone.

I've never heard about cleaner for a MAF sensor. If you decide to clean the MAF sensor make sure you use the cleaner for it and not brake cleaner. A MAF sensor is essentially a small computer, if you get something on it that is caustic or damaging then you might be out $200 for a MAF sensor.

[Allan R]

Originally Posted by Olds64

I was thinking it might be the IAC motor as well. This was a common place for carbon to build up on the early to mid 90s cars. Ford had a similar problem, they just called their's an Idle Air Bypass. It is SUPER easy to remove the throttle body and clean the back of the throttle plate and the IAC motor. I think the gasket for the IAC and throttle body is about $8.00 at Auto Zone.

I've never heard about cleaner for a MAF sensor. If you decide to clean the MAF sensor make sure you use the cleaner for it and not brake cleaner. A MAF sensor is essentially a small computer, if you get something on it that is caustic or damaging then you might be out $200 for a MAF sensor.

Hey Jesse!
Long time. Ok I need some info about this IAC motor. Both you and bcracing seem to be on the same page here. Now, where the heck is it on a 3800 series 2 and what does it look like? If you've got a tech manual or pic send it to me on a pm or post it here and I'll print it. Talked to Peter today and he suggested it might be the IAC also, but said to first think about changing the plugs. I've got NGK platinum in it now with only 37000 miles on them, and the car has no problem with acceleration or stumble when driving. He says that GM recommends copper plugs for higher mileage units, and thinks this might be a better way to start troubleshooting. Don't understand this. Do you? Glen suggested I hook it up to an OBD 2 to see if I can get a fault code like a faulty relay. Problem is I don't have an OBD 2 and it's usually about 90 bucks to get one hooked up and read out.

About the MAF? Yeah, you're right. But 200.00 is a little on the light side. They're a little more than that up here. Don't worry, if I clean it, I'll get some electrical parts cleaner and spray it down. Nix on the brake cleaner. From everything Pete says, it's not likely the MAF. Gonna stop by the parts store tommorrow and pick up some NGK copper plugs and a new PCV. I change the PCV about every 5000 miles just to be safe. You wouldn't believe the one I took out when I got the car. It was one solid gummy bear. I'm also going to give a shot of air down the PCV intake to break any crud loose that may be in there. I'm not going to touch the MAF unless I have to. Maybe I can find a good one at the boneyard next time I go out. Usually they sell computer sensor stuff for around 25 bucks or less. Read somewhere to look for a car that was in a crash. More likely to be the cause of being in the boneyard than engine failure.

This car is starting to get to me. Its getting to the point of not knowing what the next thing is that will go wrong. Like the AC that went wonky in the late summer. I'm not fixing it. AC is never cheap to repair. And this car has mostly electronics for AC. I know its not new, but this particular car seems to have been plagued with issues. Built on Monday? It doesn't know how lucky it is that I happen to be an Olds guy. I just tallied up the repair bills over the past 5 years and almost fell out of my socks! More than $12,000.00. Crap! Our vehicle tech just stopped by my office today and asked if I was still interested in his 2002 Lincoln LS. I'm starting to look at what's going to cost less and be more reliable. Man, I just hate having a moneypit. Need to win a lottery here, and soon!

[meoff]

as stated before the GM top engine cleaner is the cleaner to use and is safe for the MAF and can be used to clean the pintle on the IAC also!(best to pull the IACoff and wipe pintle down with the cleaner and spray in the pintle seat and wipe also)on your vehicle the MAF is right on the throttle body that is a black box assembly,approx 2"x3".another thought came to mind to your problem!
have you replaced the battery,or disconected or had a situation that the vehicle needed jump started recently?Not positive about the year you have but I'm pretty sure yours has the idle learn circuit programmed into the computer.in another words the vehicle has to learn it's idle.I worked on these vehicles at the dealership when they were new and dealt with a lot of drieabilality issues.to make sure it's not the computer guessing what it's gonna do--disconnect the battery for a minute or so and reconnect.
then be sure all accessories are off-A/C,radio,heater,etc.set parking brake
start engine and immedietly place shifter in drive without ever touching the throttle and allow to idle in gear for 10 minutes.shift to park and shut off and restart and put right back in drive and let idle 5 minutes again without touching the throttle.at this point the computer should have learned the idle circuit.if you have other probs then you will still have the surging you are referring to.then I will need to know the TPS reading at idle from a scan tool.or there is a way to adjust minimum idle but is used as a option if there is slop in the throttle plate etc.make sure you use the idle learn after you clean as stated in my last post.I will keep an eye on your post here till you get it fixed!any questions just ask.

[OLDSRALLYE350]

Throw the ngk plugs in the trash and put ac plugs in have removed more ngk plugs for idle problems in the last 10 years than can count. may not be your problem but why create one. Sounds like idle searching going on its usually caused by a vac leak, spray intake to head area with throttle body cleaner with the motor running, if there is a leak should see a rpm change either increase or smooth out. The only way to pinpoint the mass air flow is with a lab scope or test with a known good sensor. Do believe there is one vac lead from motor to firewall that develops a leak in the rubber part at fire wall tee.

[Allan R]

Originally Posted by meoff

as stated before the GM top engine cleaner is the cleaner to use and is safe for the MAF and can be used to clean the pintle on the IAC also!(best to pull the IACoff and wipe pintle down with the cleaner and spray in the pintle seat and wipe also)on your vehicle the MAF is right on the throttle body that is a black box assembly,approx 2"x3".another thought came to mind to your problem!
have you replaced the battery,or disconected or had a situation that the vehicle needed jump started recently?Not positive about the year you have but I'm pretty sure yours has the idle learn circuit programmed into the computer.in another words the vehicle has to learn it's idle.I worked on these vehicles at the dealership when they were new and dealt with a lot of drieabilality issues.to make sure it's not the computer guessing what it's gonna do--disconnect the battery for a minute or so and reconnect.
then be sure all accessories are off-A/C,radio,heater,etc.set parking brake
start engine and immedietly place shifter in drive without ever touching the throttle and allow to idle in gear for 10 minutes.shift to park and shut off and restart and put right back in drive and let idle 5 minutes again without touching the throttle.at this point the computer should have learned the idle circuit.if you have other probs then you will still have the surging you are referring to.then I will need to know the TPS reading at idle from a scan tool.or there is a way to adjust minimum idle but is used as a option if there is slop in the throttle plate etc.make sure you use the idle learn after you clean as stated in my last post.I will keep an eye on your post here till you get it fixed!any questions just ask.

Interesting. I assume that this idle learn circuit should be done after the engine is warm? Or should it be done cold? After 10 or 15 minutes of idling the point would be moot. Yes, this 95 (built in Nov of 94, sold and in service at Barrie Ont on Dec 12, 94) is chock full of electronics and Mr. Puters. LMK on the warm/cold issue and I'll give it a shot. BTW the battery is less than 3 years old. Your solution sounds like a Dr. prescribing non invasive surgery. I like it.

[70 cutlass s]

I would stay away from 2002 Ford anything in 02 they had trans problems and bad head gaskets. I work for a part supplier for Ford and shouldn't say it but it's the truth. I like what Meoff said sounds like pretty good advice. The OBO 2 scan tool won't tell you anything unless spend a lot of money on one with all the bells. The cheaper ones are only good with engine light on they can read the code. If the engine light is off sol. Might want to check your belt tensionor it's worth a look. If the spring is weak it's not keeping good tension on the belt at low rpm could have voltage problem that would cause your idle to drop. If your going to buy a Ford go with 05 or newer or 00 and older can't tell why but trust me 01-04 everyday at Ford was a Monday.

[Olds64]

Allan, the IAC motor is on the side of the throttle body. The easiest way to find it is trace your throttle cable to the throttle body, then you will see a small component on the side of the throttle body held on by two machine screws with an electrical connector going to it. That is your IAC motor.

IMHO, you should buy the throttle body gasket at the auto parts store and remove the throttle body (4 bolts) and IAC motor (2 machine screws) for a cleaning before trying anything else. I've done this on all of my newer cars with good results. After 100k+ miles the metered orifice in the IAC motor gets filled with carbon and no longer provides good air flow.

[wolfman98]

Originally Posted by Allan R

!
almost fell out of my socks! More than $12,000.00. Crap! Our vehicle tech just stopped by my office today and asked if I was still interested in his 2002 Lincoln LS. I'm starting to look at what's going to cost less and be more reliable. Man, I just hate having a moneypit. Need to win a lottery here, and soon!

Yeah it does not take long for those repairs to add up. I am going to fix my 90 Astro to give to my 17 year old and I have probably that much or more into it. My mom drives a 2003 Lincoln LS and it has the 3.9 litre V8. I believe this motor was with jaguar collaboration and has the 5 speed auto. Never had problems with the motor or drivetrain yet just one idiot light that would not go out and they had to replace a sensor.it is RWD but has very little ground clearance and sucks going through any amount of snow.It is however a blast to drive on clear roads and is very quick and nimbal.

[Allan R]

Originally Posted by meoff

......another thought came to mind to your problem!
have you replaced the battery,or disconected or had a situation that the vehicle needed jump started recently?Not positive about the year you have but I'm pretty sure yours has the idle learn circuit programmed into the computer.in another words the vehicle has to learn it's idle.I worked on these vehicles at the dealership when they were new and dealt with a lot of drieabilality issues.to make sure it's not the computer guessing what it's gonna do--disconnect the battery for a minute or so and reconnect.
then be sure all accessories are off-A/C,radio,heater,etc.set parking brake
start engine and immedietly place shifter in drive without ever touching the throttle and allow to idle in gear for 10 minutes.shift to park and shut off and restart and put right back in drive and let idle 5 minutes again without touching the throttle.at this point the computer should have learned the idle circuit.if you have other probs then you will still have the surging you are referring to.then I will need to know the TPS reading at idle from a scan tool.or there is a way to adjust minimum idle but is used as a option if there is slop in the throttle plate etc.make sure you use the idle learn after you clean as stated in my last post.I will keep an eye on your post here till you get it fixed!any questions just ask.

Hi there meoff,
Since CO has not been working well lately, I'll bring you up to speed with what's happening. First, I did what you suggested with the idle learn circuit. That had very little effect. One thing I need to clear up b4 going on, the engine is not "surging". It starts well cold and runs at about 1240-1250 rpm until all 6 light bars (electronic dash) on the left side are lit. It then drops to about 810 rpm. In gear it drops to 710 initially, then drops down to 680, then 660 and sometime 650-620. The idle is still relatively smooth, but you can tell that its way too low and the engine is struggling to stay going.

I disconnected the battery completely and checked both terminals and leads. Super clean. Put on some "No corrode" and tightend the leads back up. Started the car (warm) and in drive with park brake on for 10 minutes. Engine off. Restart and followed you load suggestions with AC. Not much improvement. I read on the web that the GM IAC resets if you turn the key to the "run" position for 20 seconds, then "off" for 10 seconds, followed by a restart. Then they say to run the car through 5 cycles of varying rpms up to 3500 to let the ECM monitor and learn.

Anyway, at this point in time I'm about to try cleaning or replacing the IAC. The parts store says $52.00 for a new one. From what I've read, my IAC could be working, but carboned up and not getting proper signals from the ECM to regulate properly at low idle when accesories are kicking in.

I took a picture of my engine and labeled what I think are the MAF, IAC and something I have no clue about (I call it WTH). Is my label right? I'm so tempted just to replace the unit because the car has over 270,000 km on it. (169,000 miles) That's a lot of wear on an electrical motor.

Is this pic right?


Hope you can log on to get this. Anyone else who knows if it's labelled right let me know asap. I'd like to have this up and running by Sunday afternoon. Thanks for your help

[70 cutlass s]

The MAF and IAC are correct. The other is the TPS throttle position sensor. I was going over my notes and some time ago. I had fix a car that had a problem with the IAC. The O-ring failed on it. I took it out and cleaned the IAC and replaced the O-ring. That were the notes ended so I guess that fixed it. I didn't remember working on that one.

[Olds64]

70 Cutlass S is correct. The IAC and MAF are labeled correctly, the other component is the TPS. It seems that the nut directly above the IAC motor is one of the nuts that holds the throttle body on the upper intake manifold. Go ahead and take off the throttle body and clean it thoroughly. While you have it on the bench you can remove the IAC motor and MAF sensor and clean them as well.

[Allan R]

Originally Posted by 70 cutlass s

The MAF and IAC are correct. The other is the TPS throttle position sensor. I was going over my notes and some time ago. I had fix a car that had a problem with the IAC. The O-ring failed on it. I took it out and cleaned the IAC and replaced the O-ring. That were the notes ended so I guess that fixed it. I didn't remember working on that one.

Thx for the info. I went out this morning to the parts store and had to order the IAC. They said they'll call around 11:30 when it gets in. Man that's great when you can order parts on a Sunday, they pick it from the warehouse and ship it by 9:30 to the store. $52.88 NIB IAC. Figured that a cleaning may not be enough. Looking at the picture I posted, it looks like the IAC screws have been off before, for what and when I don't know. So to be safe, I'm putting in a new one.

Originally Posted by Olds64

70 Cutlass S is correct. The IAC and MAF are labeled correctly, the other component is the TPS. It seems that the nut directly above the IAC motor is one of the nuts that holds the throttle body on the upper intake manifold. Go ahead and take off the throttle body and clean it thoroughly. While you have it on the bench you can remove the IAC motor and MAF sensor and clean them as well.

Nice to have confirmation Jesse. This IAC seems to be straight in on the TB. What a lot of other forums recommend is just cleaning the pintle seat with a clean shop towel. I have electrical parts cleaner for the job and I'll clean the IAC plug connections too. I'll have to go to GM and get a TB gasket. How do these get carboned up? It looks like they're on the outside of the TB were there shouldn't be any carbon.

On the down side to getting this done, just after I got back from the parts store and gas fill up for the wifes car, one of the garage door springs busted! Heard it from inside the house it was that loud. Worst part is that I don't have winders to release the tension on the other side spring. Also the lift wire derailed off its pulley and won't let me lift the door even with the traveller disengaged. Door repair company said they would do an emergency call for min 2 hours overtime, just to get the car out of the garage, not to fixit. Screw that. I'm going to have to take tommorrow off so I can get the springs and a set of winders. So my IAC project will be put on hold until at least tommorrow or Tuesday. The wife can use my Olds until we can get her car out. I'll have to take the bus and train again.

[Olds64]

Bummer to hear that your garage door broke. I would be hot if mine broke! We had a new one installed in February. Good luck with that.

The IAC pintle seat gets dirty because it is a metered orifice that regulates a vacuum leak at idle. Whenever you shut off the car the engine is still hot and the burned carbon goest up the intake manifold and causes carbon to collect on the back side of the throttle plate and in the metered orifice of the IAC pintle seat.

You can easily clean it with an old toothbrush and carburetor cleaner. Definitely use eletrical cleaner on the connectors going to the IAC.

[Allan R]

Originally Posted by Olds64

Bummer to hear that your garage door broke. I would be hot if mine broke! We had a new one installed in February. Good luck with that.......

Well, after 4 phone calls and no answer or return call from 3 of the big local companies, I got a smaller contractor. Yea!!! No problem, I'll be out this morning" he says. Cool, I'm thinking. I don't have to waste the whole day. I can go into work at noon. Noon comes and goes. At 1245 I call this guy (and I'm a little pissed) and ask him if he's wearing a watch, or did he forget about me? "Nope" he says, "I'm just finishing this job way over on the south side of the city". So I remind him that he said he'd have me fixed before lunch, and the wife is leaving for work around 3. "No problem", he says, "I'll have it done way before then". I feel better. "Call me when you're on your way", I say. (jeopardy theme runs in the background). Where the hell is this guy? I wonder as I nervously look at the clock for must be the 200 th time now. It's almost 2:15. I'm reaching for the phone to call this joker when it magically rings. "I'm on my way" he says. "Should be there in 45 minutes to an hour". I don't need to say what I was thinking about that call.
Anyway, he shows up at 3:10 and looks over the problem. "So it won't open?" he asks. I felt like handing him his sign, but instead I politely said, "Oh sure it opens, I just get terribly lonely and enjoy having guys drop by for a beer once in a while". He looks at me. "Of course it doesn't open" I say. "Why do you think I called you? And, one more thing" I added "You put any scratches or dents in that Oldsmobile and you're not getting paid".

Long story short: This guy finally solves the riddle and gets the door fixed. 2 springs replaced, new steel rollers and adjustment to the eyes and door sensitivity and it's back in business. "How do you want to pay?" he asks. With a straight face I tell him, "Well seeing as how you used some of my tools and you were really late, I don't really want to pay at all". He looks at me like I have leperousy, and just stands there for a minute. So I let him off the hook. "I'll use my VISA, ok?". So he goes to his truck and writes out the invoice. Brings it back to me about 10 minutes later. $482.33 I look at him, then the invoice, then him again. "So tell me" I say, "just how many shares of your company am I buying here?". I don't think he understood, so I just signed on the line. Took him almost 2 hours to do the job, but he only charged for 1 hour. I wasn't expecting a whopper of a bill. Figured it might run 250 or so, but not this much. What can you do? When you're bent over a barrell, the only thing that makes you smile is that sooner or later it's gotta stop....

Well it works, the wife isn't stranded, my boss hates me....... All is good in the world again.....

[Allan R]

Originally Posted by bcracing

Sounds like the IAC (Idle Air Control) solenoid may be either getting weak or is carboned up. It is a stepper motor, what it basically does is create a calculated vacumm leak in the throttle body which adjusted the idle speed. You can remove it and clean the end of it, and the passage in the throttle body, that may take care of it.

Took the IAC out today. OMG! it could hide in a bag of BBQ bricquets and you'd never find it. The pintle was out to about a 1 3/8" distance from the base. The new IAC has a new O ring, and another replacement one. I put in the new IAC, reconnected it and fired up the car. It made 3 popping / clicking sounds at first, but then nothing, and the idle was pretty smooth.

Originally Posted by dan2286

I had a similar problem when I had my 00 Grand Prix with the same engine. Sometimes the idle would fluctuate and would sometimes start bucking while driving. When sitting at lights with the car in gear, the rpms would rise and sometimes would stall out. It rarely threw a code and when it did, it would be a misfire code. Eventually it started throwing a maf sensor code. Replaced that and the problem went away.

It did start with the fluctuating rpms at idle, then after awhile it started bucking while driving. Maybe that is something to look out for.

The MAF sensor was ok. There's only 2 screws to undo and 2 wires to clean.

Originally Posted by bcracing

Well I just got done working on my sons 97 GP 3800, his was doing the samething, The IAC had already been replaced, so wasn't that, turned out to be the MAF sensor. Replaced that and it idles like brand new. But his did throw a service engine soon light.

Mine does too now, but it still erratic rpms under load. I might have to take it for a run. The info sheet for the new IAC says that to reset the pintle, run the engine for 1 minute and then shut it off. I did this and the problem is still there.

Originally Posted by meoff

as stated before the GM top engine cleaner is the cleaner to use and is safe for the MAF and can be used to clean the pintle on the IAC also!(best to pull the IACoff and wipe pintle down with the cleaner and spray in the pintle seat and wipe also)on your vehicle the MAF is right on the throttle body that is a black box assembly,approx 2"x3".another thought came to mind to your problem!
have you replaced the battery,or disconected or had a situation that the vehicle needed jump started recently?Not positive about the year you have but I'm pretty sure yours has the idle learn circuit programmed into the computer.in another words the vehicle has to learn it's idle.I worked on these vehicles at the dealership when they were new and dealt with a lot of drieabilality issues.to make sure it's not the computer guessing what it's gonna do--disconnect the battery for a minute or so and reconnect.
then be sure all accessories are off-A/C,radio,heater,etc.set parking brake
start engine and immedietly place shifter in drive without ever touching the throttle and allow to idle in gear for 10 minutes.shift to park and shut off and restart and put right back in drive and let idle 5 minutes again without touching the throttle.at this point the computer should have learned the idle circuit.if you have other probs then you will still have the surging you are referring to.then I will need to know the TPS reading at idle from a scan tool.or there is a way to adjust minimum idle but is used as a option if there is slop in the throttle plate etc.make sure you use the idle learn after you clean as stated in my last post.I will keep an eye on your post here till you get it fixed!any questions just ask.

I did this 2X already, but with the old IAC (carboned up) still in. I'll have to do it again and see what happens. I also plan to replace the spark plugs with copper core. The parts store didn't have any AC Delco's so I bought some Champion Copper Plus. Factory spec says to gap at .060 On an older engine do you still do this, or should it close up to say .055 or less? I've heard it argued both ways.

Originally Posted by Olds64

The IAC pintle seat gets dirty because it is a metered orifice that regulates a vacuum leak at idle. Whenever you shut off the car the engine is still hot and the burned carbon goest up the intake manifold and causes carbon to collect on the back side of the throttle plate and in the metered orifice of the IAC pintle seat.

You can easily clean it with an old toothbrush and carburetor cleaner. Definitely use eletrical cleaner on the connectors going to the IAC.

Just like you and the others said. I also cleaned inside the TB. When I took off the old IAC I hooked it up to my Multimeter. On 200 Ohms setting, it showed a reading of 49 on the first 2 terminals. On the next 2 it read 47. Both well in the acceptable range which means the IAC motor is good. I cleaned it up really good and put it on my spare parts shelf so it's ready for the next time I need it.

I'd like to thank all you guys for the great support and coaching on this project. The next step is to see whether the idle learn circuit will work properly with this new IAC, or whether I need a new ECM. Anyone got any thoughts on that?