96 S10 2.2 Idle Issues - Pulling my hair out

Hopefully someone can help me out with my 96 s10 2.2 5 speed. I dont know where else to look. Here is the deal.

Start truck up (cold start) no problems at all. Once truck warms up and is shut off (off for maybe 10 minutes) then it starts up just fine. However within a few minutes sitting at idle it will start to die, sputter, and usually stalls. Always starts right up after. If you give it some gas when it starts sputtering then it goes away and does not reoccur. No problems while driving, just at idle.

Sometimes it will not die but will catch itself and the rpms shoot way up then come down after about 5-10 seconds.

I gave it a full tuneup not long ago (new plugs, wires, ignition coils, fuel filter, pvc valve)
I have replaced the TPS, IAC, and the fuel pump (for a different problem). Fuel pressure is staying constant at about 45 psi.

One of the old wires had alot of resistance and when I replaced it with 4 new wires the stalling was not as bad which leads me to some kind of ignition problem. Also the last time it did this it threw a P1441A EVAP System during Non-Purge. I disconnected the purge valve so nothing could get into the intake and it still stalls out. Scanner gives no codes or failures when it happens.I think the stalling caused vacuum issues with the purge valve.

Can anyone help me out? I dont know what else to try. Im using a Matco ProScan Plus scanner (OTC Nemisys). Thanks

Have you watched the data stream for the Mass Air Flow sensor ?
What are the fuel trims doing during this episode ?

Just some thoughts.

Also if your are a professional what do you think of the OTC scanner ?
We use the Snap-On Solus.

On this engine there is no mass air flow sensor as I believe it was from 94-97 on the 2.2s. What should I be looking for as far as the fuel trims? Ive never been really able to catch them as its happening.

Overall im pleased with the proscan. I am not a professional, just a do it yourself kinda of guy. I love learning about cars and have built a couple racecars.

On the Data screen is there a "STFTrim" parameter ? If the reading is positive , above 0, the fuel is rich. If the reading is negative, below 0, then the fuel is being reduced to the injectors.

I was thinking maybe Engine Coolant Temp. sensor.

But that should have thrown a code.

Have you put a fuel pressure gage on the engine as well to see what the fuel pressure is doing during this ?

Comming off of the Air Box, there isn't a MAF sensor there ?

Ok so your just after the short term fuel trim. I will get the scanner on there when it happens and get the numbers.

The coolant sensor is also new as I replaced it awhile back because the connector got damaged. Indeed there is no MAF on these engines. In 98 they used them on the 2.2s but not on the 96's.

I probually shoud have mentioned that both o2 sensors are new as well.

Ok been playing around today and got some more info. First off fuel line pressure stays constant at just below 50 psi at the rail when this occurs. No drop offs or changes.

It appears that this occurs when the truck goes back into closed loop mode. When it starts up it is open of course, but the problems start when the scan tool says its going into closed mode. At this point my short term fuel curve jumped to -18.8% and the IAC count position goes way up to 60. Spark advance is slightly retarded to 15 deg. Engine Load jumped up to 100%. Somehow it is getting way too much fuel. Once it died and the other time it shot the idle way up like it does at which time I saw it shot back into open mode and stayed there idling and had no problems. This time it produced a new code P0507B along with the old code P1441A

Thus this is occuring when going to closed mode but only after the truck has been started once and warmed up some. And thus far I have produced 2 codes.

P1441 Evaporative Emission (EVAP) System Flow During Non-Purge
P0507 - Idle Air Control System RPM Higher Than Expected

IAC and TPS are new. Any ideas? :iceslolan

Ok, watch the Manifold Absolute Pressure sensor voltage if the MAP sensors voltage goes up without depressing the accelerator pedal it is telling the PCM that engine load has increased when in actuality it has not. This will cause a rich condition like the one you saw. The fuel trim went negative because the O2 sensor told the PCM there was too much fuel and not enough oxygen for a 14.7 to 1 air/ fuel ratio.

Did you clean the throttle plate when you installed the IAC ?

Let me know or Private Message me.

The MAP is used in both Open Loop and Closed Loop Modes, but watching the input is a good idea.

You might also want to verify a reasonably correct signal from both the CTS and MAT. You might especially want to look at the O² signal.

Yes, the '96 has no MAF, but is strictly a speed/density scheme of operation. This requires an accurate MAP input, accurate MAT and CTS, and accurate O² signals. Since these engines also use the highly suspect "Flexi-Joint" on the exhaust manifold, make sure the O² sensor is not exposed to dilution from external air leaks.

The fact that it all goes south as soon as the PM hits Closed Loop should be a big indicator that one of the inputs is way off, but not quite enough to be out of tolerance and set a DTC.

Looks like we are getting somewhere. :popcorn:

Ok the CTS is new, replaced this summer, I accidently broke the connector. It seems to quickly change to temps and appears accurate.

The MAT, or IAT as I am used to, is not new. I did notice that it appearred a little sluggish but then Im not entirely sure what it should read. What are some normal numbers? I have a aftermarket air intake and the temp read about 100 degree lower than the IAT. I would assume that the IAT should hang pretty consistant with the outside air temp should it not?

As for the MAP I did notice that upon starting the engine load was 26% without depressing the pedal. Shouldnt it be only about 3% or so? Can someone tell me how much vacuum I should be seeing from the MAP at idle for this engine?

Thanks guys!!

Check your PM.

Checked the values on the sensors.

My MAP sensor at engine off is 4.18 volts, which seems about right as im at 3800 feet here. Engine on it is about 1.2 volts at idle. The thing that seems strange with the MAP is that as soon as I start the engine the engine load is 23-26%. Is this normal?

CTS and IAT both are on temperature wise and react quickly to changes.

One I did notice the last time it stalled was that it threw a failure code (Did not give a SES light though) of P1406D. P1406 is egr valve pintle position circuit as the description. I have pulled the EGR awhile back and cleaned it, not much carbon was there.

Is it possible I just have a sticky EGR valve when it gets warmed up?

Check your PM.

Pulled the EGR valve and cleaned it up. Did not appear to have much carbon and the valve moved fairly smoothly. Im fairly certain that the MAP sensor is the issue now as when the surging start the engine load and map voltage so way up and bounce all over. I have a MAP sensor on the way so hopefully that fixes it up. BTW what is a normal amount of vacuum in these 2.2s? I am only getting about 15 in.

Normal vacuum should be 19 - 21 in. HG.
Let us know if the MAP sensor was the culprit.

I replaced the MAP sensor and the truck ran better and the fuel curves leveled off. However the truck stalled out again last night the second time I started it as it did before. :uhoh:

Man im bummed. Any other ideas what could be the problem ?

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 :smile:
I really appreciate anyones help on this! Greatly appreciated!

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.

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.

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?

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.

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.

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

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!