Diagnostic Aids
WARNING: This page is about a different car, the 2002 Oldsmobile Aurora. However, it is still accessible from the selected car via links, so may be relevant.
Fuel contamination, such as water or alcohol will affect fuel trim. A bad MAF sensor can cause a rich condition. See DTC P0101: MASS AIRFLOW SENSOR SYSTEM PERFORMANCE . Using scan tool, review failure records. If an intermittent condition is suspect, see INTERMITTENT CONDITIONS under SELF-DIAGNOSTIC SYSTEM.