I just replaced a head gasket on my 91 fbird w/305 TBI and auto trans. The timing has been a total headache. I noticed that when the EST connector was connected, keeping the car running while in gear was a challenge. Even idling was a problem. However when I disconnected it and set the timing to factory spec and left it disconnected the car ran good and gave me no problems other than the SES light coming on. It just made me wonder if my Computer was bad. Is this the case? Let me know because any advice would be much appreciated. Thanks!

 

Might be the ESC module rather than the ECM itself. The module is located driver side firewall, on the bracket that houses the fuel pump and fan relay. Maybe it has a bad connector, or you bumped a wire going to it when doing the head gaskets, or something.