It's a 92 LT1 vette (6 speed) and is all stock as it sits now. I have a popping through the exhaust which I have determined to be because it is running rich at idle. Tried a new map sensor, coolant temp sensor reads good, new ignition module and coil, new O2 sensors, checked for leaks that would create a false lean, and put on new exhaust manifold gaskets. Fuel pressure reads good as well. This has happened ever since I owned the car and I can't figure out what it is. I do have Autolite 104's in it because of a nitrous kit, but obviously i don't spray it right now with this issue. You can see it running way rich on a scanner, and then if I unplug the MAP sensor while it is running, you can see it lean back out and it idles perfect. I know it is running on default values at this point, but doesn't that eliminate it being an ignition problem? I can't drive it with no map sensor, but can't figure out what the problem is. Car runs great at full throttle and above 2000 rpm or so. HELP!!!!!!

 

Anyone have any ideas????

 

Have you considered the possibility of a faulty lifter or a sticky exhaust valve? Dump enough air into the exhaust and its a "false lean".

 

I have thought about that. Although, why would it idle perfectly when I unplug the MAP sensor? Doesn't that rule out the possibility of a mechanical problem, and point to a sensor or something that provides input to the computer to alter fueling?