Section 19 (Engine Controls - Tests W/Codes): Summary
WARNING: This page is about a different car, the 1993 Volkswagen Passat. However, it is still accessible from the selected car via links, so may be relevant.
If no hard fault codes (only "sporadic" codes) are present, driveability symptoms exist or intermittent codes exist, proceed to the TESTS W/O CODES article for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.) or intermittent diagnostic procedures.