Diagnostic Aids
WARNING: This page does not describe the selected car, but rather 7 other vehicles, including the 2002 Pontiac Grand Prix, 2002 Pontiac Bonneville, 2002 Chevrolet Monte Carlo, 2002 Chevrolet Impala, and 2002 Buick Regal. However, it is still accessible from the selected car via links, so may be relevant.
An intermittent condition could be caused by an improperly installed or damaged EVAP canister purge valve or a temporary blockage in EVAP canister purge valve. To repair a blockage in the EVAP system, see EVAPORATIVE EMISSION SYSTEM CLEANING in appropriate REMOVAL, OVERHAUL & INSTALLATION article.