3800 stalls then surges when warm

I have a 1999 Grand Prix GT with a 3.8 L engine. The car starts fine and runs well when cool (under 170 degrees) but then stalls and surges and sometimes even dies after the engine has warmed up. While driving down the road, it seems to happen most often under acceleration, but will also stall at idle. Whether the transmission is in or out of gear does not make a difference either, as the engine will sputter and stall at start up and in neutral. I have heard it might be a bad temperature sensor somewhere, but no one can be exact. I have replaced the coolant temperature sensor/switch, but it made no difference. Any input would be greatly appreciated.

I have a 1999 Grand Prix GT with a 3.8 L engine. The car starts fine and runs well when cool (under 170 degrees) but then stalls and surges and sometimes even dies after the engine has warmed up. While driving down the road, it seems to happen most often under acceleration, but will also stall at idle. Whether the transmission is in or out of gear does not make a difference either, as the engine will sputter and stall at start up and in neutral. I have heard it might be a bad temperature sensor somewhere, but no one can be exact. I have replaced the coolant temperature sensor/switch, but it made no difference. Any input would be greatly appreciated.


As a starting point how many miles are on your GP GT?

It has roughly 83,000 miles on it, I just changed the fuel filter, air filter, and pcv valve. The car was in great working order, then all of the sudden started doing this after it was warmed up.

I'm assuming that you've done the basics such as spark plugs and wires in addition to what you've done and the SES light is off. How is it at cruising speeds? I believe that what you're actually seeing relative to temperature as the engine warms up is the ECU/PCM computer going between closed and open loop mode. When the engine temperature exceeds 145 degrees and all input from various sensors is proper it switches to closed loop mode. Fuel injector pulse modulation is controlled via the ECU through the 02 sensors which provide feedback. At idle or accceleration, especially WOT (wide open throttle) it switches to open loop mode where it depends on input from other sensors.

I could be wrong but you have classic symptoms of a defective MAF sensor or possibly a clogged or partially clogged CAT convertor. To illiminate the MAF (Mass Airflow) sensor which is critical in open loop mode just disconnect it. Then take it out for a spin and see if the problem improves or fixes itself. You can run a short period of time with it disconnected at least for troubleshooting purposes. The ECU will then use pre-programmed MAF tables based on fixed RPM. If it fixes the problem get a replacement MAF sensor. If not have your CAT convertor tested for exhaust flow.

Hope the info helps. Good luck!