tex70

I have a 72 olds cutlass. I thought it would be a good idea to put STP cleaner in my gas tank since I filled it up with gas. I don't know if the STP has caused problems, but now my car is running rough and when coming to a stop or slowing down my car shakes like it wants to turn off. If I brake without giving gas my car will shut off. Anyone know what I can do to get my car running right again? Before I put the STP my car ran great, I just thought it would make it run better. Do ya'll think my fuel pump is the problem or my fuel filter??? Thanks in advance. Carlos-

telli_tell

What type of cleaner exactly did you use? If your fuel pump is going out it will be leaking.

Jim's rare 80

Hi. Just curious. Do you have power brakes? If so, check vacumn line to your brake booster. If the car is idling in park, and you step on the brake, does it still stall? I am asking because you would have to add a lot of STP to screw up a fuel system. Let us know.
Jim.

tex70

Well I used Stp Treatment. Yes I do have power brakes.A mechanic did tell me that my brake booster was leaking,but could that be the problem for my car turning off on me? I'll turn on the car and when putting it in reverse or drive the car starts to stall like it wants to shut off. I have to keep my foot on the gas and on the brake at the same time so it won't shut off on me. When driving it a straight long distance the car does okay until I come to a stop then it starts to stall.

$tryker

It's doubtful the STP is your problem. It does sound like a vacuum leak.
Spray some carb cleaner around that booster and vac. line while it's running. If the idle picks up, there's your leak.

tex70

Well, yesterday I changed out all plugs and wires and distrubtor. I even cleaned out my carb, and the car is still running like crap. However after taking it for a test drive I noticed that my brakes are harder to press. Now im thinking it may be the brake booster.

Chumley

Have you tried turning up the idle speed and/or adjusting the idle mixture? My car has the same problem(although it does not stall) I think I have a bad idle circuit in the carb, or possibly worn throttle shaft/plate. I'm going to put a new carb on at any rate. Chumley

tex70

Yes I tried adjusting the carb, and for a little while it would run great. As soon as I put the car in reverse or drive it starts to stall wanting to shut off. I have to keep my foot on both the gas and brake when going into reverse or drive. If I don't keep my foot on both the gas and brake my car will shut off. Same thing when Im driving and coming to a stop sign or light, I have to keep my foot on the gas and brake. I am now in the process of changing out my brake booster, someone told me that my booster may be why my car is stalling.

Jim's rare 80

Hi. My guess is the booster. Did you check engine vacumn? Let us know how it goes. Jim.

tex70

I ordered the booster from O'Rileys auto parts and I wont get it until Tuesday. Im keeping my fingers crossed. I hope the booster will solve the problem. I'll keep ya'll posted......

Oldsmofjord

Hi there

I have the same problem.

I have the 81 Cutlass LS with the V6. Not sure about the carb though....

I had it adjusted at the workshop and it ran great. Then suddenly as I started it up again yesterday I could even get it out of the parkinglot - it just shut off. I had to drive back and forth alittle first and then it got going. Then when I got to my destination, after idling for 5 mins, it died out again....

I adjusted the carb again and it ran great. Then after some driving back and forth the idle speed went down yet again (!) and I fear the same things will happen - that it dies out.....what can all this be ?

$tryker

I'm confident that Tex70's problem is a vacuum leak of some sort, the carb cleaner would confirm that. As for Oldsmofjord, a vac. leak is possible, but an open egr would do the same thing. Tex70's engine wouldn't have an egr. Good luck to both of you.

Oldsmofjord

Open egr ? Pls explain

side note : the engine gets rather hot after all this driving around, and it's especially hot when I encounter the false idle speed and shutdowns.....

$tryker

An egr (exhaust gas recirculation) is a device that that lets a small amount of exhaust enter the intake manifold during highway speeds. It does not function while city driving (under 45mph). If the valve is stuck in open, the engine would not idle well. You'll find it close to the carb, in the middle of the intake. It will have a vacuum line on top.

Hope this helps

tex70

Dang, there is a lot of helpful information here. Well I should find out today if the booster was my problem. I know my booster was leaking pretty badly, I just don't understand how it would affect engine performance. Once I change out my booster I'll keep ya'll updated. Damn booster was a pain to get off.

Oldsmofjord

This sounds logical

I have found out about the EGR thing - looked into Hayne's book for my Olds and I found everything there. I'll take a look under the hood 2nite

tex70

Well, I changed out my booster and master cylinder. My car is running a whole lot better now. I just drove it down about 3 miles for a quick test and the car is not stalling anymore. Thanks to everyone for helping me out.

Oldsmofjord

Some said that I can remove the EGR completely, and just tighten the hoses attached to it......will this work ?

Oldsguy

The reason the booster affects engine performance is that it is a big storage device for engine vacuum. If it leaks then you essentially have a vacuum leak in you engine just as if one of the vacuum lines were leaky or not connected on top of the manifold. This faulty vacuum messes up the operation of the carburetor since it operates on pressure differential between the engine and the ambient pressure (vacuum). And, secondly, the weak vacuum signal affects your advance unit on your distributor so you have incorrect timing advance.