Diagnostic Aids

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.

Fuel contamination, such as water will effect fuel trim.
A malfunctioning Mass Airflow sensor can cause a rich condition and set this DTC. See DTC P0101: MASS AIR FLOW SENSOR PERFORMANCE under DIAGNOSTIC TESTS in SELF-DIAGNOSTICS - 4.8L, 5.3L & 6.0L EXPRESS & SAVANA - GASOLINE article.
Use a scan tool in order to review Failure Records. If an intermittent condition is suspected, see INTERMITTENT CONDITIONS under SELF-DIAGNOSTIC SYSTEM.