94 Corolla stalls when hot

Trying to help a relative that is 2 1/2 hr drive away. Her car stalls and runs rough when it gets to operating temp. They have changed plugs, wires, etc. and the mechanic said it was the computer, so that was changed, but no change (didn't sound like a computer problem to me, but!!!!). :disappoin Anybody have any ideas? :banghead: Maybe the distributor? Thanks for any help.

Being that the PCM was verified to be good, the difference in PCM function cold vs warmed up is that once warmed up the PCM will run closed loop, using O2 sensor feedback to control injection duration -- if the O2 sensor is faulty, it could be giving the PCM a bad signal (the sensor outputs voltage) that could cause the stalling.

You would think this would throw a code, but I once forgot to re-connect the (front main) O2 sensor harness after a repair, and the CEL never illuminated, even after several trips.

The key is the difference in function/performance cold vs warmed up -- It could also be the CTS (coolant temp sensor), or its wiring -- in this case, the PCM will always think the engine is cold (and run the cold start "rich" program), so it will be fine until the engine warms up, when the over-rich PCM program will cause bogging, etc... this over-rich condition will possibly damage the O2 sensor if it continues for an extended period. Essentially, the engine will not "know" when it has warmed up. This should also cause an immediate CEL indication.

So check them both. In any case an over-rich condition will usually also be accompanied by a strong fuel odor.

*add: On my '95, the TEMP gauge sending uint, and the PCM CTS sensor are independent of each other, so the dash gauge will read fine even if the CTS connected to the PCM is faulty or disconnected.

:grinyes: Thanks for the info.. Was thinking about the O2 sensors. Will be going over to where the car is this weekend, and see if I can resolve this for her. Thanks again. Pat