It seems as though the air/fuel mixture is too rich, and pressing on the gas pedal allows the added incoming air to lean out the mixture. If the factory sealed throttle stop adjustment has been moved to a more closed position, in a misguided attempt to reduce the idle speed; this will definitely cause the problem you describe. The second most likely possibility is a bad idle air control valve. Otherwise, this condition is probably caused by a bad throttle position sensor. It could also be caused by a clogged fuel filter, a plugged PCV valve or PCV hose, or a defective air charge temperature sensor.
Monday, March 4th, 2013 AT 9:47 PM