1990 3.1 randomly runs/doesn't

title pretty much says it. here are my experiences in trying to pinpoint a problem.

when it starts, it runs/idles great. then after a variable amount of time (couple min up to 40 min), it just dies completely like i just shut off the key, in park, while driving, doesn't matter.

when it doesn't run, it cranks and fires, but then just dies completely immediately after. however, if i stay on the gas i can keep it running but very rough. then when i let off the gas it will just die completely. now one time i started it, stayed on the gas to keep it running (though very rough as i mentioned), and it smoothed out and stayed running as i let off the gas. i got out of the car, walked around for a sec, then it just died out of nowhere.

now i'm no automotive expert, let me know if i need to be more specific or if there is any other information i can provide to help you help me :)

sounds like an ignition module or crank position sensor, what doesn't make sense is if you can give it gas, it will stay running, it thhen almost sounds like a fuel delivery problem. Unless the high temperatures and high compression might be sufficient to ignite the air/fuel mixture without spark. Get a spair spark plug and an issistant, start it, let it run untill it dies, pull a wire off of a plug, and put it on the extra plug then lay the plug on a good ground. And have the assistant crank the motor over, watch the gap on the plug to see if it is in fact sparking If it is, and is still not running, its fuel related. if it starts and runs on 5 cylinders, let it run untill it dies again. and keep and eye on the grounded plug. Myself im leaning towards Crank Position Sensor. You can also take a hair dryer and heat up the ignition module, and then attempt to start it, if it doesnt the module could be your problem as it runs great untill it wrams up, but dies when it does. Very common. It just doesnt make sense that if you give it gas when dying you can keep it running. I guess i dont really know. Just dont start throwing parts at it, try to diagnose it. you can also hook it up to a fual pressure guage and watch the pressure when the car stalls out.