1995 5.0 running rich with surging idle.

[Twood98]

i have a 95 gt 5.0, that is running very rich and bounces off about 500-1000 rpm at idle also backfires and stumbles when revving. happened Randomly With no Signs or Warnings, was driving through town Red light after Red Light then it just decided to start stumbling when i accelerated after shift.
Replaced: MAF(also checked voltage was okay)
Injectors
EGR
throttle Position Sensor
Fuel Pump
all O2 Sensors and checked voltage to them also good.

checked the vaccum
checked for fuel leaks
only thing i can think is maybe a fuel problem. once i unplug the fuel pump the car runs perfect until its out of fuel. pulled only one code with snap on code reader and it was for contaminated MAF which was then replaced,

 

[Christian Cornwell]

Do you have a chip in the computer? They can cause these types of problems. Does sound like it could be fueling also by what you're saying. Have you changed the fuel filter? I haven't seen one plug that I can recall but it could be. Have you tried resetting the computer by leaving it unplugged for 15+ minutes? Could just need a reset.

 

[VibrantRedGT]

Sounds like your trouble shooting has landed you at the fuel system. Since you've unplugged the fuel pump or relay and the idle cleans up then keep going in this direction.

Bad fuel, change fuel filter, empty the fuel tank and while you're there upgrade your fuel pump. If all else fails you've eliminated these items too.

 

[jozsefsz]

Check your fuel pressure and for presence of fuel in the fuel pressure regulator vacuum line - could be a bad fuel pressure regulator.