Hesitation/Sag/Stumble

SYMPTOM DESCRIPTION:
Momentary lack of response when the accelerator is pushed down. Can occur at any speed. Usually most severe when accelerating from a stop or initial cold start up. Engine may stall if condition is bad enough.




SYSTEM OR COMPONENT TO CHECK

COMPUTER INPUTS/OUTPUTS

CHECK:

- FULL THROTTLE SWITCH AND/OR THROTTLE VALVE POTENTIOMETER (where applicable): Defective switch, poor connection or damaged wiring to control unit.
- AIR MASS SENSOR: Defective sensor, poor connection or damaged wiring to control unit.
- COOLANT TEMPERATURE SENSOR: Incorrect or defective sensor (wrong resistance value), poor connections or damaged wiring to control unit.
- CONTROL UNIT: Poor connections, or defective control unit.

Refer to Computers and Control Systems.



FUEL SYSTEM

CHECK:

- FUEL PUMP: Check for insufficient fuel pressure or volume from pump.
- FUEL PRESSURE REGULATOR: System pressure too low.
- FUEL INJECTORS: Clogged or stuck injector, poor spray pattern.



IGNITION

CHECK:

- SPARK PLUGS: Check for fouled spark plugs, improper gap, heavy deposits, damaged or burned electrodes.
- SPARK PLUG WIRES: Check for high secondary resistance, or wires arcing to ground.
- IGNITION TIMING: Check distributor basic adjustment.
- IGNITION DISTRIBUTOR, CAP, AND ROTOR: Check for cracks, arcing, moisture, rust deposits or high resistance through rotor.

Refer to IGNITION SYSTEMS.