I might suspect the fuel filter and/or plugged cats or pre-cats. RacerX10: I couldn't tell if you had an ATX or not, but ATX tours will not rev past 4K in Park or N. (Tranny/diff. protection built into PCM) The CEL light will go out if the error condition that caused the fault clears up. EGR passages in UIM behind TB clog up and are a common cause of EGR related error codes. Remove the TB and clean up with TB cleaner and soft rags. Plugs and/or wires also could be a cause of the stumbling. The IMRC should open normally at around 3800 RPM and can be tested in the driveway by operating the throttle by hand and watching the linkage.
