96 S10 2.2 Idle Issues - Pulling my hair out

[wickedude]

Ok some new info, I found out that there are some cracks in the header near the upstream o2 sensor that I previously did not notice.

I rechecked the readings the other day with the new map sensor in and when hot the IAC count was 28.

I was just out playing with it and there is a pattern.

On a cold start it never does sputter or stall.

On the second start after its been left like 5 minutes or so is when it does it, but only if left at idle. Driving around it is just fine.

If the engine is left very hot I have not noticed it do it, but again it is only noticable if you start and leave it idling, or maybe stop at a stoplight for a prolonged period.

Ok back to when it does do it,

The IAC count was 66
Long term fuel trim was -12.5 %
injector Pulse was 1.4 msec
Engine load was 25%
So the PCM is really trying to lean the engine here.

I noticed that each time the engine tried to die and caught itself the upstream O2 went full rich (1.0 v), and then the engine recovered. It then went back into closed mode and tried again. Sometimes it wont "catch" and it does die.

This is where im confused on the issue. My thinking is the leaking header is letting oxygen get to the upstream o2 sensor, causing the PCM to get a lean (low voltage) o2 signal when in fact the exhaust is not lean.

But the PCM then is leaning the mix out which causes the engine to try and stall out? The engine starts to die , kicks back into open mode, goes full rich, richens up and catches itself sometimes.

If the o2 is getting air why is the PCM still trying to lean out the mix? Sorry im confused here
I really appreciate anyones help on this! Greatly appreciated!

[Wags391]

I believe I've been having the same problems and I know for a fact my down pipe exhaust doughnuts are leaking. I'm about to replace them, if I can get the damned bolts out. Same symptoms could be caused by the same problem. I'd fix the header.

[dg89]

I have a Pont g-am and sounds similar to the prob I was having. All it was for me was the fuel pressure regulator was leaking. I replaced that and my starting and stalling problems went away.

[wickedude]

Sorry to bring up an old thread but I still cant resolve this issue.
It has gotten so bad the truck wont idle when its hot.
I just replaced the fuel pressure regulator, all 4 fuel injectors with new injectors, and a new fuel filter. Pressure is constant. It is still doing the stalling when hot. Never one the first start though. Could this be some kind of pcm issue when it gets hot?

[wickedude]

I swapped in a used pcm and it did the same thing once it was hot. Im still thinking this is electrical somehow. The reason I say this is because when the engine is surging and about ready to die I can turn the key off. Then when I start it back it up it idles just fine and smoothly. Usually it will not start the surging again for 10-15 minutes. If this was a fuel issue I would think the surge would start again as soon as I restarted the truck.

Any other ideas? I am so frustrated on this thing.

[wickedude]

Im still thinking this is somehow electrical as it starts right back up. My question is could this be a crankshaft or camshaft sensor issue? Ive been researching cavaliers that have had similar issues with these sensors. Ive replaced about everything but not the CPS or CKPS sensors.

[whitcheywoman13]

I was having the same problem. Although I had problems starting (cold start) would take almost a half hour. Once it got started...noticed that RPM would not go past 4000 with my foot to the floor. After driving, would do fine on highway but as I got into traffic would spit and sputter. Took to a mechanic and he said the fuel pump was going. Found out that the problem was not pump, but electric wire that goes to pump. (remove bed and check wiring with test light have to strip wire). If it lights up its getting voltage and you should hear the pump come on..no bad pump. The pin in the connection to the pump was bent...was not straight in the middle. I'm thinking this was causing the intermittent voltage which made the pump not get the right amount of fuel. Also, the mechanic who checked and said pump was bad said to not to let it get past half a tank of fuel as this causes the pump to work harder. Found another problem after replacing tons of stuff, the throttle body control valve was bad and replaced that. NO MORE PROBLEMS THANK GOD!!! hope this helps

[wickedude]

Just wanted to follow up on this post. I was still having this issue and it was getting worse with the hot weather here.

I noticed on the scan tool that the upstream o2 seemed to be lethargic after the engine had been run and heated up. This was very noticeable after letting the engine cool for 20 minutes or so. As someone suggested, as soon as I entered closed loop, the surging started.

I also noticed that ac delco lists two o2 sensors for my s10, AFS 21 and AFS 22. AFS 22 was listed as a heated sensor though I didnt know that was possible for a single wire sensor to be heated. Anyways I decided to change the sensor and bought a AFS22 and instantly my fuel curves were much leaner and I had much more sensor activity. My surging issue has now stopped. Thus my upstream o2 sensor was bad, but just not bad enough to set off a trouble code it seems. Thanks for everyones help!