I have a 91 Caprice with an L03 engine. This car ran fine until about 2 weeks ago. Once the engine has been running about 25 minutes it just dies. This happens whether I let it idle or drive it for that length of time. It sets no codes at all. I found a vaccuum leak in the map sensor line and changed the hose, no change. I also changed the fuel filter,and the fuel pump relay. I have been told the ICM under the cap is notorious for intermittent problems. The engine usually starts right up then stalls about 5-10 minutes later. When it stalls on the highway you get the sudden jerk then it dies. I'm wondering if the O2 sensor or the TCC could be the real culprit here. Any suggestions?

Does the car start to smoke? Black smoke would be indicative of running rich, possibly beacuse the temperature sensor is giving wrong ifo. I have had 2 Caprices with the same problem, both times it was the temp sensor for the computer, not the guage.

I haven't noticed any black smoke. The sensor you're speaking of is it the IAT sensor in the air cleaner cover?

I haven't noticed any black smoke. The sensor you're speaking of is it the IAT sensor in the air cleaner cover?

The IAT only controls the flap for the heat riser. The sensor he's talking about is the engine temperature sensor, located usually on the thermostat housing (has a black and yellow wire attached).

see if the oil pressure sensor leaking through the connector terminals, sensor could be shorting out and causing the pcm to shut off the fuel pump- the purpose of that is if the oil pressure is under 4 psi, it will shut the fuel pump off and saves the motor... but i tried that it worked for couple of days and stalling problem happening again, so i have to check the car out again.