I am the original owner of the car and I have taken good care of the car. Last tune up 2500 miles ago. All belts and hoses replaced 5000 miles ago.
Car starts up and runs perfectly. After about 30 minutes of city driving the car will get into a " stalling mode". While in motion the car runs and sounds fine. When stopping, remove foot from gas pedal and depress the brakes, the car stalls. If I put car in neutral before applying the brake, the car will not stall. I turn ignition off then back on and restart the car with no problem. The car idles fine on its' own. While I have the brake pedal depressed and put the car in " D" rive, the car stalls out. I have to get the idle up around 800 rpm (by pressing gas pedal), in order to put car in " D" rive without stalling. After the engine cools down for about 30 minutes, it will come out of the " stalling mode".
What has been done to resolve the problem:
Had a mechanic check out car:
engine -very good.
coolant system -very good.
computer diagnostic - all good, no errors.
verified idle booster functions when Air Con. Turned on -ok. Replaced " idle air control valve" - NO HELP.
Mechanic ran out of idea's, do you have any suggestions?
Some GM cars have an Torque Converter Clutch (TCC) electric lockup. When the car is in closed loop, above 35ish MPH, brakes off the ECM will command the TCC switch to lockup. When you depress the brake, or go below 35MPH the ECM commands the TCC to unlock. Sometimes the TCC will get stuck in the locked position causing it to stall.
You can check on the side of the transmission for a square 4 prong weather-pak connector, try unplugging it and see if it still stalls. This will disrupt the physical connection to the ECM and prevent the ECM from grounding the TCC.
If the TCC is bad it must be replaced, generally you do not have to remove the transmission for this.