I have an 85 trans am and its got 78,000 miles on it and it has a problem noones been seemed to be able to figure out. When i start the car, it jumps all the way up to 2 thousand rpm's and after staying there for a couple seconds it works its way down to the normal 800 and when its at idle there it idles terribly. it shudders and the rpms go up and down about 100 rpms in either way and it isnt smooth.
Thats just where the problem starts. it drives fine. until i brake hard. then it stalls. it startrts to hesitate and goes down to 4 or 500 rpms and just quits. giving it gas does nothing. and then to start it back up it takes a couple minutes of cranking before itl start and opwerate as normally with the bad idle and the 2000 rpm start. it also does this when i take an on or off ramp really fast.
Its giving me a code 54. and ive done a lot to try and figure out what that is. ive pulled the plenum off and cleaned that out and all the sendors out, replaced vaccuum lines, even the hard ones, cleaned the trottle body and runners out, cleaned the egr and tested it and its working fine, all the sensors in the trottle body, and ive decarbonized the cylinders and this has all made it run smoother and more powerfull, just with the same problem.

Please help me, you guys are my last hope. i love this car b ut its really starting to frustrate me.

 

code 54 is low voltage on the fuel pump circuit, you need to check the fuel pump relay and all the associated wiring for worn out parts or damaged wires, possibly the fuel pump itself.