90 Grand Prix stalls like its going into diag mode

I have a 90 Grand Prix and a week a so ago it started stalling while i was driving. The "Check Engine Soon" and "coolant low" light flickered when this happened along with the fans under the hood popping on and off in sequence. I checked the computer for codes and the only one that showed up was 12. I had a remanufactured motor put in about 5 mo. ago and it has been fine up until now. I checked all the fuses that were related to the ECM, secodary "hot' battery post under hood with ECM and Fuel Fuse and the one in the glove box. When the car does run the idle is high , about 2500 rpm.

Before i get into replacing the ECM or the MEM-CAL i was wondering if anyone knew of anything less expensive i could replace befoe doing so?????

The high idle makes me wonder if you need to do an idle relearn, but kinda doubt it since the engine has worked fine up until now. You could try this, http://www.60degreev6.com/index.php?p=pages&pid=74, since it is free. The idle air control could possibly be dirty or bad. Go to autozone.com and check out the repair info for your car. I believe they tell how to clean and test the IAC. It's pretty easy. It does sound kinda like the computer is acting up, but the stuff above doesn't cost anything to try so could give it a shot before dumping money on the computer. Oh yeah, have you checked the connections to the computer? Saw a statistic on a show once saying that roughly half of the computers that get replaced are still good. They most likely just had a bad and/or corroded connection and that sometimes just unplugging the connectors, then plugging them back in would fix the problem.

Thanks for the tips! But im still having the problem. I took the computer out, including the Prom, and checked all of the connectors. I even did the lean relearn but im still haveing the same problem.

One thing i did remember before all this started happening was that when i started the car smelt rich. I was wonderingt if the O2 sensor could be the cause of all my troubles? I never changed it since i bought the car in 96.

I had the exact same problem. I spent a lot of money before they found out it was the O2 sensor.