Hesitation, Sag, Stumble

WARNING: This page is about a different car, the 2004 GMC Sierra and 2004 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.

Checks	Action
DEFINITION: The vehicle has a momentary lack of response when depressing the accelerator pedal. The condition can occur at any vehicle speed. The condition is usually most severe when attempting to make the vehicle move, as from a stop sign. An extremely severe condition may cause the engine to stall.
Preliminary Checks	Refer to Important Preliminary Checks in Symptoms - Engine Controls .
Fuel System Checks	Test for proper fuel system pressures. Refer to Fuel System Diagnosis . Inspect for low pressure during moderate or full throttle acceleration. If the fuel pressure drops below specification, there is possibly a low or high pressure regulator fault or a fuel system restriction. Test for proper EVAP purge system operation.
Sensor Checks	Test for proper TP sensor operation. A TP sensor that does not respond quickly and accurately to throttle plate movement may cause this symptom. Test for proper MAP sensor operation. A MAP sensor that does not respond quickly and accurately to manifold pressure changes may cause this symptom.
Ignition System Checks	IMPORTANT: A higher secondary ignition voltage is required to operate the vehicle on CNG than on gasoline. Test for proper secondary ignition system voltage output using only the J 26792 Spark Tester. Inspect for fouled spark plugs. If fouled spark plugs are indicated the reason for the fouling must be found and corrected. Test for faulty spark plug wires. Test for an open ignition system ground - if equipped.
Additional Checks	Review service bulletins for module programming updates. Inspect for manifold or air induction system leaks. Test for proper generator operation.