Hesitation, Sag, Stumble

Definition: The vehicle has a momentary lack of response when depressing the accelerator. The condition can occur at any vehicle speed. The condition is usually most severe when trying to make the vehicle move, as from a stop sign. The condition may cause the engine to stall if it's severe enough.

Preliminary Check
Refer to Important Preliminary Checks. Testing and Inspection

Fuel System Checks

^ Check the Manifold Absolute Pressure (MAP) sensor response and accuracy.
^ Check for water contamination in the fuel.
^ Check the Canister Purge system for proper operation. Refer to Evaporation Emission (EVAP) Control System Diagnosis and EVAP Control System Diagnosis. System Diagnosis - EVAP Control
^ Perform the fuel injector coil test. Refer to Fuel Injector Coil Test. Fuel Injector Coil Test
^ Perform the fuel injector balance test. Refer to Fuel Injector Balance Test. Fuel Injector Balance Test
^ Check for low fuel pressure after a cold start or during a moderate or full throttle acceleration. If the fuel pressure drops below specification, there is possibly a faulty fuel pump or a restriction in the fuel system.

Ignition System Checks

^ Check for faulty spark plug wires.
^ Check for fouled spark plugs.
^ Check for an open ignition system ground. Refer to Enhanced Ignition System Diagnosis. System Diagnosis - Enhanced Ignition

Additional Checks

^ Check the Service Bulletins for PROM updates.
^ Check the generator output voltage.
^ Check the Exhaust Gas Recirculation (EGR) Valve operation. Refer to Exhaust Gas Recirculation (EGR) System. System Diagnosis - EGR