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Misfire Isolation

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.
  1. Start engine. Disconnect IAC motor. Using insulated pliers, remove one spark plug wire from a spark plug, and ground it against engine.
  2. Note engine RPM as wire is grounded. Reconnect spark plug wire. Repeat procedure for all cylinders. Stop engine, and reconnect IAC motor.
  3. If engine speed dropped equally (within 50 RPM) on all cylinders, refer to ROUGH, UNSTABLE OR INCORRECT IDLE symptom. If there was no engine RPM drop or no excessive variation on one or more cylinders, check spark on respective cylinder(s).
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