3.1 L problem

I've been banging my head on this one.
My 1990 grand prix has a "Check Gauges" light that comes on the moment the engine gets to normal operating temp. All gauges look fine. There are no codes. When this light comes on, the engine will not idle. Even if your running on the highway at 60 mph and you let your foot off the throttle, it dies instantly. It has no codes. I've had the alternator, the idle air control valve, throttle body, and cat convertor replaced. Problem still exists. Its in the shop now having the ECM replaced. Luckly these parts arn't costing me anything cause the used car dealer is covering it. I love this car. Its mint condition with only 57,000 miles on it. Anyone have a clue what might be causing this?

check for a bad catalytic converter. and check the egr... other than that, i havent a clue

my 91 had sort of the same problem, you had to really hold the gas down to keep it running otherwise it would just die. this problem was attributed by two things. 1. bad fuel injectors. 2. Computer causing car to inject fuel incorrectly. Have you had your battery disconnected lately? Whenever i disconnected the battery on my gp the computer would loose its "memory" and i would have to slowly take it up to the dealership to be reprogrammed.

Yes, I did have the battery disconnected to clean the terminals, but the problem started before that. I was also hoping when I had the battery disconnected, that it would reset the ECM but that didn't help it. I did just get a call from the garage that the ECM replacement seemed to take care of the problem of stalling, but now he said the speedo is 15 mph off.