Hesitation, Sag, 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.

SENSORS
- Check 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).
- Check Heated Oxygen Sensor (HO2S) ground corroded threads in exhaust manifold.

FUEL SYSTEM
- Check fuel pressure, use Chart A-7. Testing and Inspection
- Check contaminated fuel.
- Check EVAP canister purge system for proper operation. Use Chart C-3. Testing and Inspection
- Check fuel injectors. Perform injector balance test, use Chart C-2A. Testing and Inspection

IGNITION SYSTEM
- Check spark plugs for being fouled, or for there being faulty secondary wiring.
- Check ignition system ground (ignition control module mounting bolts).

ADDITIONAL CHECKS
- Check for correct PROM. (See Service Bulletins.)
- Check engine thermostat functioning correctly and proper heat range.
- Check generator output voltage. Repair if less than 9 or more than 17 volts.
- Check for air leaks between Mass Air Flow (MAF) sensor and the throttle body.