I have a problem with my 1991 firebird formula TPI. The original problem with the car was whenever it was driven, the car ran fine, but when it came to a stop, it would begin revving between 1100 and 200 rpms, jumping all over. Sometimes the car would die and usually restart, but it would stay running only when you go into neutral and rev when coming to a stop. Sometimes the vehicle would not restart at all until you let it sit for about 15 minutes, then it would run fine. I was told the problem was the distributor, so i replaced it. Since then, the vehicle runs terribly. The timing is correct and i also bought new plug wires as well and have checked all spark plugs. The car will start, but idles really crazy. It will idle fine for 10 to 20 seconds then begin jumping and backfiring. I thought replacing all the TPI gaskets and cleaning the runners, plenum, and manifold, as well as replacing the TPS would help, but I have had no luck. I recently replaced the fuel pump as well. Please help!!! Thanks

 

First place I would have looked for an answer is the IAC valve, idle air control valve. 4 wire plug on the throttle body.

 

I had the same problem, so I bought a new idle air valve, about a 90 dollar part.