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 Diagnosis By Symptom/Preliminary Checks. Testing and Inspection

SENSORS
Check:
^ Throttle Position (TP) sensor - For binding or sticking. Voltage should increase at a steady rate as throttle is moved toward Wide Open Throttle (WOT).
^ Heated Oxygen Sensor (HO2S) ground (corroded threads in exhaust manifold).

FUEL SYSTEM
Check:
^ Fuel pressure, use Chart A-7 Fuel System Diagnosis. Related Tests, Information and Procedures

^ Contaminated fuel.
^ Evaporative Emissions (EVAP) canister purge system for proper operation. Use Chart C-3 Evaporative Canister Purge Valve Check. Chart C-3 EVAP Canister Purge Valve Check

^ Fuel injectors. Perform injector balance test, use Chart C-2A Injector Coil/Balance Test Procedure. Chart C-2A Injector Coil Balance Test Procedure

IGNITION SYSTEM
Check:
^ Spark plugs for being fouled, or for there being faulty secondary wiring.
^ Ignition system ground (ignition control module mounting bolts).

ADDITIONAL CHECKS
Check:
^ For correct Programable Read Only Memory (PROM).
^ Engine thermostat functioning correctly and proper heat range.
^ Generator output voltage. Repair if less than 9 or more than 17.3 volts.
^ For air leaks between Mass Air Flow (MAF) sensor and the throttle body.