Section 133 (Engine Controls Self-Diagnostics - 4.3L): Summary
WARNING: This page is about a different car, the 2003 GMC Savana and 2003 Chevrolet Chevy Express. However, it is still accessible from the selected car via links, so may be relevant.
If no hard fault DTCs are present, driveability symptoms exist or intermittent DTC(s) exist, diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.). See SYMPTOMS in TROUBLE SHOOTING - NO CODES - 4.3L CHEVY EXPRESS & SAVANA article.