94 Grand Am Shuts Off Immediately after starting.

I was driving one day and with no symptons or anything the car just shut off. I got it towed home and it would start right up but immediately shut off revving it or not. I put the computer to it and 2 out of 5 scans it said the alternator. I changed my alternator and found out it was over charging cause I had it checked before i got a new one. It ended up blowing the ignition module so I changed that and the car ran great for 2 weeks. Then one afternoon I went to leave and the car did it again, started right up then shut right off. This time though if I rev it up and keep the rpms above idol the car stays on but as soon as it hits idol it shuts off. Their is spark, plenty of fuel getting the the engine. I checked the battery incase a cell blew when the alternator was over charging and it was fine. Then for some reason i unplugged the alternator and the car fires right up and runs but my battery would just drain right down so i can't drive it around like that. so i figured it must be the computer so i put in a new computer but i continued to have the problem. I checked all vaccuum lines too no leaks. Anyone have any suggestions?

This seems to be a repeated question on the 3.1L/3100. You might want to check the crank position sensor. Had the same problem with my car. Replaced the fuel filters, fuel pump, control module, plugs, wires, and the egr valve. But it turned out to be the crank position sensor. Hope this helps.

I kinda with evan, the CPS tends to be a recurrent prob. on older GA's.

Thanks I'm gonna look into that.

I'm having trouble finding the CPS. Any help?

It's on the engine block on the firewall side.

http://www.autozone.com/servlet/UiBroker?ForwardPage=/az/cds/en_us/0900823d/80/0e/57/01/0900823d800e5701.jsp
click on this link as knifeblade left for you scroll down to the 3.1L and itll show you where it is and how to remove and replace. Its between the block and the pass side strut tower. behind the harmonic balance. What did you think they would make it easy to replace.

I put in a new crankshaft position sensor car still don't work. It starts and then shuts right off but if you unplug the alternator from the computer the car starts and keeps running. What does that mean?

i really dont know but how did you come up with the idea of unplugging the alternator?

Have your alternator checked, if its overcharging sometimes the ecm will shut it down to prevent damage.

I don't really know, i knew i put in a new alternator and i figured maybe it was shorting out somewhere when its hooked up,

I can get the car to run without the alternator but once the alternator is hooked up it don't run. I keep taking out alternator and trying different ones from autozone to no avail.

I can get the car to run without the alternator but once the alternator is hooked up it don't run. I keep taking out alternator and trying different ones from autozone to no avail.
I would disconnect the battery, disconnect the alternator, and do an ohms test on the hot line to the alternator and make sure it is not shorting to ground. If it is, trace the wire and fix the short.