What would cause a car to shut down at 30mph or less when it is warm?

I don't know but I have a 1991 Grand Am LE with nearly 200,000 miles on it that's having the exact same problem. Someone recommended I try cleaning the idle air control valve. I haven't done it yet, but I'll let you know if it works. It's nice to know that someone else is having the same problem.

I would suggest that you take your car in for a computer diagnostic. You may have a computer chip that is going bad. I would also suggest that you use Berryman's fuel treatment in your gas tank. It only costs a few dollars and it might help. If the fuel treatment does not work,the computer diagnostic is your best bet. You can call around to find the best price for a computer diagnostic.