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 throttle linkage and/or TPS do not stick or bind.
Ensure initial ignition timing is properly set.
Check engine idle speed (both base and ECM idle).
Check Idle Air Control (IAC) system. Check for foreign material in IAC bore. See DIAGNOSTIC AIDS in CODE 35 chart in appropriate G - TESTS W/ CODES article.
Check EGR system for proper operation.
Check park/neutral switch circuit. Ensure park/neutral switch is properly adjusted.
Check power steering pressure switch circuit.
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.
If rough idle occurs only when engine is hot, check PCV valve for proper operation. Check evaporative emission control system. Check for proper spark plug gap and engine compression.