Section 10 (Engine Controls - Tests W/Codes - 3.1L Engine): Summary
WARNING: This page is about a different car, the 1998 Pontiac Grand Prix, 1998 Chevrolet Monte Carlo, 1998 Chevrolet Lumina, and 1998 Buick Century. However, it is still accessible from the selected car via links, so may be relevant.
If no hard fault codes are present, driveability symptoms exist or intermittent DTC(s) exist, proceed to TESTS W/O CODES - 3.1L article for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.) or intermittent diagnostic procedures.