Note on Intermittents
WARNING: This page is about a different car, the 1990 Cadillac Fleetwood and 1990 Cadillac DeVille. However, it is still accessible from the selected car via links, so may be relevant.
At idle, manipulate the EGR solenoid connector, ECM connector and related wiring. The EGR solenoid should remain energized (circuit No. 435 grounded) to block vacuum to EGR valve/vent vacuum to atmosphere. Listen for a change in idle quality.
Drive vehicle at TPS between 8-15 degrees, and engine at 1450-1650 RPM to try to duplicate code. With a hot engine (idling), apply and release vacuum to EGR valve to check for EGR valve sticking in up or down position.
Remove EGR valve and check for excessive carbon build-up that would restrict EGR flow, or foreign materials holding EGR valve open. Check vacuum pump output and vacuum hoses for pinched, cut, kinked, misrouted or blocked hoses.