Hesitation, Sag or Stumble

DEFINITION
Momentary lack of response as the accelerator is pushed down. Can occur at all vehicle speeds. Usually most severe when first trying to make the vehicle move, as from a stop sign. May cause engine to stall if severe enough.

PRELIMINARY CHECKS
^ Perform the careful visual / physical checks as described in Preliminary Checks.

FUEL SYSTEM
^ Check fuel pressure, refer to Procedures / Diagnostic Charts / Chart A-6 Fuel System Diagnosis. Testing and Inspection
^ Check the Throttle Position Sensor (TPS) for sticking and binding. Voltage should increase at a steady rate as throttle is moved toward WOT.
^ Check the Manifold Absolute Pressure (MAP) sensor response and accuracy, refer to Procedures / Diagnostic Charts / C Charts / Manifold Absolute Pressure (MAP) Output Check. Testing and Inspection
^ Check for contaminated fuel.
^ Check fuel injectors. Perform injector balance test, refer to Procedures / Diagnostic Charts / Chart A-7 Poppet Nozzle Diagnosis. Testing and Inspection
^ Check the EVAP canister purge system for proper operation, refer to Procedures / Diagnostic Charts / Canister Purge Solenoid. Testing and Inspection

IGNITION SYSTEM
^ Check the spark plug wires for being faulty.
^ Check spark plugs for being fouled.
^ Check ignition system ground circuit 453 or ignition timing.

ADDITIONAL CHECKS
^ Check Service Bulletins for correct PROM.
^ Check generator output voltage. Repair if less than 9 or more than 16 volts.
^ Check Exhaust Gas Recirculation (EGR) valve operation, refer to Procedures / Diagnostic Charts / C Charts / EGR System Check. Testing and Inspection