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.

Check thermostatic air cleaner damper door for proper operation. Also check for a clogged air filter.
Check cooling system thermostat for proper heat range and operation.
Check coolant sensor for shift in calibration. See COOLANT TEMPERATURE RESISTANCE VALUES table in SENSOR RANGE CHARTS article.
Ensure speedometer is properly calibrated.
Check engine compression.
Check for dragging brakes.
Ensure A/C is not always on.
Ensure initial ignition timing is properly set. Check EST and ESC for proper operation.
Check TCC for proper operation.
Ensure air pump output shifts to catalytic converter upon signal from TVS. Check for faulty electrical and/or vacuum circuits.
Check exhaust system for restrictions, such as a damaged or collapsed pipe, muffler or catalytic converter. See EXHAUST SYSTEM BACKPRESSURE under MECHANICAL INSPECTION in BASIC TESTING article.
Check O2 sensor for silicone or lead contamination.
Remove spark plugs, and check for wet plugs, cracks, improper gap, burned electrodes or heavy carbon deposits.