B4dFi5h

Im working on a 2003 Chevy Impala with a 3.8 v6. The car will start and run for about 5-10 min before idle starts to break up and eventually stall out. The car will start again after it stall but wont stay running or even idle, i have to hold it to about 2,300 RPM for it to continue to run. We have replaced the MAF, IACV, and the TPS. Tonight i tried to hook up my MODIS to check for codes. There were no current codes or stored codes and could not get the car to run long enough for it to even trigger one. I checked the FPR and its in good shape and hold fuel pressure. We also looked into the throttle body during cranking to see that it is still getting fuel. Im looked online and i had read about the anti-theft protection triggering similar problems but the owner just checked and said there were no anti theft lights flashing at any time. I am now thinking that it may be a clogged cat. Someone had said a crank or cam position sensor maybe even the ECM but im not sure of those do to the fact it starts and runs flawlessly for a good period of time before the symptoms start... any other ideas besides setting a rag on fire in the gas tank?

Fabrik8

Does the behavior change depending on when the engine is warm versus cold? SO is that initial 5-10 minutes of idle with a cold engine?

B4dFi5h

we cant keep it running long enough to get it to temp.

B4dFi5h

when we first started it up to work on it is when it runs the best. So yes it runs better cold.

Fabrik8

Check the coolant temp sensor, which runs to the ECU. That is responsible for a lot of cold-start idle control. The temp gauge will likely have a different temp sender, although I have no idea how GM does that.

B4dFi5h

Ill def check that. Any other ideas?

Fabrik8

Could be an O2 sensor, if the problem is occurring when the ECU transitions from open loop to closed loop idle. That will usually happen at a certain temp also.

JDM74

the temp gauge is just a fancy idiot light run by the ECU more than likely. There should only be 1 temp sensor. What you need to do is do a cold start with a scan tool hooked up and watch coolant temperature and see if it rises as it should as the car warms up or if it is reporting some wonky value.

ej1995

Those cars have that weird ICM that sits under the coils. Those things are notorious for breaking down after some time.

B4dFi5h

im def gonna check out those ICMs. Sounds very fitting.