My son's car is a 2008 Grand Prix. 3.8 L. Stalls at operating temperature

change the fuel filter... if there is one. also change the thermostat incase it may be stuck open.

also... what conditions do the stalls occur? coming to a stop? climbing? post a bit more info to give more insight. engine runs cold could be too much coolant flow; so i'm thinking the thermostat could be bad..

It stalls randomly. At first it seemed to stall on deceleration. Now it stalls just idling and in park. At first it could get him to school and back. (2.5 mile trip) most of the time no problem. Then if he came home and went back a short time later for practice it would sometimes stall. Now it seems to be getting worse. The guy at the shop said it will stall within 5 minutes of starting and just idling in the shop. It will start again in about 10 minutes. When trying to start it just doesn't fire right and won't catch until it cools down a little. Fuel pump tests fine. Coolant level good.

What codes come up when they scan it? Also, and this is a long shot, is the catalytic converter in good shape? Check that it's not plugged.

Thanks, the catalytic converter was changed in the last month.

what are the computer codes they got from the reader that might have been on the shop repair bill? or anything the mechanic stated?

Here are some of the codes in the last 8 months. P0120 P0403 P0405 P0107 (or P2107 bad handwriting) P0303 P0306 P0621 and the most recent from the mechanic after two weeks that cannot find the problem is P0386.

Now with the new PCM it will run for about 30-45 minutes and then stall. I drove it home yesterday and let it sit in the driveway and about 1/2 hour later it just stalls. No sputtering or anything, just stalled.

someone wrote this in another post.... seems about right. For the Pontiac Grand Prix: If the tachometer reads 0 RPM while the engine is cranking or running, there is a fault in the crankshaft position circuit that includes the sensor, wire harness, ignition control module, and engine control module. A defective sensor won't transmit the correct reluctor wheel signals back to the ICM and ECM causing improper or no spark leading to engine stalling or misfires. However, a defective ICM could cause erratic power/ground (voltage) to the sensor leading to inconsistent crank readings. Intermittent spark issues are difficult to troubleshoot. If you're just part swapping, replace the ICM first, then the CPS, and finally the wire harness.

They guy at the GM dealer swapped out the ICM and said no change, would still stall. Finally took it out of there. Took it to an electrical automotive place. They put on an ICM from a car they had there and the car has been running for over 45 minutes and driven after that for 20 minutes. They are now going to put in a new ICM and since I had a new one put in about 6 months ago, still under warranty. Is it possible to have a bad batch of ICM's? When the first one was put in, the mechanic had trouble with it, and had to put in another one. After that is when the stalling started. Why would a used one work, but the new ones not?