Possible Causes & Corrections:

WARNING: This page does not describe the selected car, but rather 35 other vehicles, including the 1992 Pontiac Trans Sport, 1992 Oldsmobile Silhouette, 1992 Oldsmobile Bravada, 1992 GMC Yukon, and 1992 GMC Vandura Special. However, it is still accessible from the selected car via links, so may be relevant.

Ensure EGR valve is not always open.
Check for proper valve timing.
Check for engine vacuum leaks. Ensure engine is tuned to specifications.
Check for faulty air injection diverter valve or check valve.
Check engine for sticking or leaking valves.
Check for fuel or water in vacuum hose to MAP sensor. Also check for restricted hose.
Using Spark Tester (ST-125), check available output voltage of ignition coil.
Check for crossfire between spark plugs, distributor cap and spark plug wires.
Check for an intermittent ignition system problem.
Check for erratic spark timing or distributor reference (RPM) signal.
Ensure initial ignition timing is properly set.