2000 2.4-Stalls after warming up.

I have a 2000 Grand Am with 205,000 miles (2.4, DOHC). It starts fine and runs fine, but after driving 10 to 15 minutes, when I stop at a light, the engine will die. It will re-start easily and will continue to run as long as I keep my foot on the gas a little. So far, I have changed the oil and plugs. I was going to try to change the fuel filter, but it is difficult to access without a lift. When I changed the oil, there was a "chocolate" haze in some areas, which I think indicates coolant in the oil, which could be from a blown head gasket. I am not sure what the oil usually looks like with a blown head gasket, so I might be mis-diagnosing here. Since I would like to avoid changing the head gasket, I bought some Bar's Leak head gasket fix, which I will try soon. I am requesting potential causes and fixes, and other diagnosing techniques that I can use.

Thanks for your help.

It sounds like the engine is lacking air at idle. The IAC should maintain the engine speed at the programmed target idle UNLESS the PCM has applied the maximum programmed IAC steps.

The other, often overlooked, source of idle air is the PCV valve. The system is designed to regulate idle air but relies upon the correct volume of air being applied through the PCV. The IAC simply supplements that air with intake air.

I would suggest a thorough cleaning of the throttle body, IAC, IAC air passages, and PCV valve and hoses as a start. Inspect all other hoses for damage while you're at it. A faulty PCV valve/system will also fail to remove moisture from the crankcase through normal operation, and this can appear as moisture in the oil, as you reported.

If that doesn't improve the condition, connection a scanner to read the target idle, mixture, and IAC counts would be helpful.

It sounds like the engine is lacking air at idle. The IAC should maintain the engine speed at the programmed target idle UNLESS the PCM has applied the maximum programmed IAC steps.

The other, often overlooked, source of idle air is the PCV valve. The system is designed to regulate idle air but relies upon the correct volume of air being applied through the PCV. The IAC simply supplements that air with intake air.

I would suggest a thorough cleaning of the throttle body, IAC, IAC air passages, and PCV valve and hoses as a start. Inspect all other hoses for damage while you're at it. A faulty PCV valve/system will also fail to remove moisture from the crankcase through normal operation, and this can appear as moisture in the oil, as you reported.

If that doesn't improve the condition, connection a scanner to read the target idle, mixture, and IAC counts would be helpful.

I cleaned the idle air control valve and it seemed to help. The car will now idle when stopped at a light, but at a low rpm. It usually idles at about 600 rpm, and sometimes will drop to about 400 and then increase to about 900 before settling back at 600. I am not sure what the target idle speed is. I think it is time to have the system hooked up to a scanner. Do I have to go to a dealership to get this done?
Bye the way, I appreciate your help. It seems like we are on the right path. While I am at it, I will also have the ignition module checked, since this problem only happens after the car warms up.

1:40 p.m. Breaking news: I just took it out for another test drive after adding some fuel injector cleaner and the stalling is back.

cold idle rpm: about 1200RPM (temperature dependant, can be lower)
normal idle rpm: 600RPM

the IAC might not be clean enought, the MAF could be dirty.
Spark plug could also be dirty/worn

cold idle rpm: about 1200RPM (temperature dependant, can be lower)
normal idle rpm: 600RPM

the IAC might not be clean enought, the MAF could be dirty.
Spark plug could also be dirty/worn

I have already changed the plugs and air filter, and this engine does not have a mass airflow sensor. I will try to take a closer look at the throttle body to see if it is clean and take another look at the IAC. I am hesitant to replace the IAC without knowing that it is bad - they cost $70. I will let you know if I get this solved. Thanks again.

If you do have to clean the MAF sensor, use a cleaner that is only for the MAF sensor. CRC makes MAF sensor cleaner, and it is good. If you do not use MAF sensor cleaner it will ruin the MAF sensor.