When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Hi to all.
Is the idle air control valve (IAC) a "rare part" or has the design changed?
I am only finding this thing at Rockauto. I've come a long way, with this top half rebuild on my Aunt's 84 Cutlass Calais 3.8l V6. I managed to get the a/c working after 10 years of her insisting she "didn't want it"... So the IAC [ ilde speed control] may haven't been put to work either for a while? Anyway I had it all just about buttoned up, after redoing all the vacuum lines, except for the Idle air kick up when a/c turns on. Turns out I had 12 volts to it; and the the points inside where also okay. I took it apart and it was pretty dried up and grungy. After cleaning and re-greasing 3 tiny gears, I also tested the small motor with 12 volts test and it too worked. So... I put it all back together and it was (began) working "great". I adjusted the "fast air idle" screw on the carb from 1800 to the 2200rpm spec. and with engine running warm, at smooth idle of 800rpm, I would turn on a.c and the ISC would slowly raise up idle to 1000. When I would turn a/c off the rpm would pop up to around 1300 just a second and then slowly drop back down to around 900. Well, that only worked for a while. Yesterday the car started running rough, and I could hear this intermittent "chattering noise" from the ISC. A/C idle kick up obviously not working either. Does the ISC "work" any other time (beside w a/c)? The only identical part I could find looks like a (one week min. wait) online order. If this is the only job this part does can I do something "temporary" in order to use the car?
Last edited by Johnny99; September 23rd, 2017 at 06:21 AM.
Reason: brevity and correct terminology
Hi to all.
Is the idle air control valve (IAC) a "rare part" or has the design changed?
I am only finding this thing at Rockauto. I've come a long way, with this top half rebuild on my Aunt's 84 Cutlass Calais 3.8l V6. I managed to get the a/c working after 10 years of her insisting she "didn't want it"... So the IAC may haven't been put to work either for a while? Anyway I had it all just about buttoned up, after redoing all the vacuum lines, except for the Idle air kick up when a/c turns on. Turns out I had 12 volts to it; and the the points inside where also okay. I took it apart and it was pretty dried up and grungy. After cleaning and re-greasing 3 tiny gears, I also tested the small motor with 12 volts test and it too worked. So... I put it all back together and it was (began) working "great". I adjusted the "fast air idle" screw on the carb from 1800 to the 2200rpm spec. and with engine running warm, at smooth idle of 800rpm, I would turn on a.c and the IAC would slowly raise up idle to 1000. When I would turn a/c off the rpm would pop up to around 1300 just a second and then slowly drop back down to around 900. Well, that only worked for a while. Yesterday the car started running rough, and I could hear this intermittent "chattering noise" from the IAC. A/C idle kick up obviously not working either. Does the IAC "work" any other time (beside w a/c)? The only identical part I could find looks like a (one week min. wait) online order. If this is the only job this part does can I do something "temporary" in order to use the car? The irony in all this, is that she never wanted the AC because she thought it put a strain on her motor.
First of all, your 3.8 motor with a 2bbl carb does NOT have an "idle air control valve", despite what RockAuto or other auto parts store catalogs may call it. IACs are used by fuel injected motors to precisely control air that bypasses the throttle body for idle control. Your car has an idle speed control that uses a stepper motor to push the carb throttle arm open to raise the idle speed.
Read chapter 6C and 6E in your Chassis Service Manual. The ISC on the V6 is constantly being adjusted by the ECM to maintain the idle speed. It is used all the time. The functioning, adjustment, and troubleshooting info is too lengthy to repeat here.
I wish I did have the factory chassis manual. I've never done this much work on these cars. When all this began I grabbed one of those $25 Chilton's and figured that would get me through a head gasket job. That, Google, and especially this group here. I'm not going to be able to buy a "Real manual " anytime soon. I suppose I'm going to replace Idle Speed Control (ISC) regardless, since it's really old and worn. I have no choice for the present, I have to get her car back. I have devoted all the time I can afford on this, for this season. I'm just glad the motor is back together and running better than it has in years!
First of all, your 3.8 motor with a 2bbl carb does NOT have an "idle air control valve", despite what RockAuto or other auto parts store catalogs may call it. IACs are used by fuel injected motors to precisely control air that bypasses the throttle body for idle control. Your car has an idle speed control that uses a stepper motor to push the carb throttle arm open to raise the idle speed.
Read chapter 6C and 6E in your Chassis Service Manual. The ISC on the V6 is constantly being adjusted by the ECM to maintain the idle speed. It is used all the time. The functioning, adjustment, and troubleshooting info is too lengthy to repeat here.
Well I got the manual and the car is running pretty good! I repaired a vacuum leak (that developed at the carb/intake) while I was waiting. I wanted to use the original EFE base gasket, but went ahead and just replaced w a plain $9 2bbl gasket for time being. There is certainly a TON of info. in that Chassis Serv. Man., and after reading chapter 6C and 6E, (about 6 times) I surprised myself and got it dialed in! Now to just see about the choke.
Is that choke electric? What is it doing on cold start?
Yes electric. I tried it this morning cold. It does, (semi rough) idle up to about 1100 until I tap pedal. Then it returns to about 700. There is just a bit of rough idle in general. Once the motor reaches operating temp it's much less noticeable, but still there. When I first put it all back together after heads went to machine shop, it was purring like a kitten. I think maybe I need to double check timing/dwell/fast idle. The only carb adjustments (beside the stop idle screw for ISC) made so far is the idle air bleed valve. This I gently seated then backed out 4 turns... Closing it down doesn't seem to change much. Right now I have that at 3 turns out. The rich mixture stop screw and the two idle mixture needles are accessible... Before I touch any of that I'm going to have to get my own timing light, dwell meter and some carb. adjustment tools. I personally have never attempted to adjust any of this before. I hope some minor adjusting may smooth it out... I'm proceeding very cautiously, because most of all this is more than I have ever attempted by myself, until now.
Last edited by Johnny99; September 23rd, 2017 at 01:49 PM.
Reason: ad pics
September 10th, 2017, 08:10 AM
ISC adjusted!
