need help with a 91 chev cav z24

I have a 91 Chevy Cavalier Z24 (automatic) with 3.1L and a V6. The car ocasionally stalls for no aparent reason. It has no problem starting again but when I try to shift it into gear it will instently stall. I have found that the stalling only occures when I have been driving for a long period of time (an hour or so), or at a constent higher speed and then trying to decrease to a lower one. This problem doesn't happen all the time, only once in awhile. Since it isn't a reguler occurence it has been very difficult to pin point exactly what the problem is. Also the check engine light speratically comes on. If you can help me at all please do. Thanks :)

I had the same problem that you are having. I took my Z24 to a mechanic and had the alternator replaced, and it hasn't stalled since. It was the weirdest damn thing. The car would start no problem. Then after a while of driving i would come to a stop light or sign and the damn thing would start to jerk back and forth and finally shut off when i would come to a stop. Right away it would start back up. As long as the car was moving it was fine. It was just when I needed to stop. I am not 100% positive that it is the same problem, but it wouldn't hurt to get your alternator looked at.

You might also want to have a Fuel Press test done. You might have a sick fuel pump.

There are a couple of things that can cause this problem..... but from what you said i'm leaning toward one more then the other. You said after you reach a higher speed and then come back down to a lower speed it will start to act up. that is a sure sign of the Transmission Torque converter lock up switch. I have the same problem on on one of my 1990 Z24's. What happens is the sensor doesnt disengauge from gear after it reaches its highest..... 3rd or 4th if you have overdrive. When you slow down and come to a stop it kills the car instantly. also when you start it up... put it in gear and let your foot off the gas it will kill too. What i did was just disconnect it and now its fine. its located on the transmission right on the front of it. it faces the radiator. you will probably have to take the air cleaner assembly out to see it, it has 4 wires going to it. I'm pretty sure its the only thing there so its kind of hard to miss. you could have it replaced but they would have to split the transmission from the engine, half the sensor is outside,.... the other half is inside. Give that a try, its easy to do, if it works then you've saved yourself a ton of headache.