Hesitation, Sag, Stumble

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

PRELIMINARY CHECKS
Refer to Preliminary Checks. Testing and Inspection

FUEL SYSTEM
CHECK:

- Fuel pressure.
- Throttle Position (TP) sensor - Check TP sensor for binding or sticking. Voltage should increase at a steady rate as throttle is moved toward Wide Open Throttle (WOT).
- Manifold Absolute Pressure (MAP) sensor response and accuracy. Refer to Diagnostic Charts/ C-Charts / Manifold Absolute Pressure (MAP) Output Check. MAP Sensor Output Diagnosis
- Water/contaminated fuel.
- Canister purge system for proper operation.

IGNITION SYSTEM
CHECK:

- Spark plug wires for being faulty.
- Spark plugs for being fouled.
- Open ignition system ground CKT 453 or ignition timing.

ADDITIONAL CHECKS
CHECK:

- Service Bulletins for PROM updates.
- Generator output voltage. Repair if less than 9 or more than 16 volts.
- Exhaust Gas Recirculation (EGR) valve operation.