Section 28 (Engine Controls - Tests W/Codes): Summary
WARNING: This page is about a different car, the 1994 Volkswagen Passat and 1994 Volkswagen Corrado. 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, diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.) or intermittent diagnostic procedures. See TESTS W/O CODES article in the ENGINE PERFORMANCE.