Hesitation/Sag/Stumble

***UPDATED BY TSB #289003, #259102.

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: Defective switch, poor connection or damaged wiring to control unit.
- AIR FLOW SENSOR AND/OR POTENTIOMETER: Defective sensor (sticking), poor connection or damaged wiring to control unit.
- DIFFERENTIAL PRESSURE REGULATOR: Defective pressure regulator, poor connections, damaged wiring to control unit.
- COOLANT TEMPERATURE SENSOR: Incorrect or defective sensor, poor connections or damaged wiring to control unit.
- CONTROL UNIT: Poor connections, or defective control unit.

Refer to COMPUTRES AND CONTROL SYSTEMS.



FUEL SYSTEM

CHECK:
- FUEL PUMP: Check for insufficient fuel pressure or volume from pump.
- PRIMARY FUEL PRESSURE REGULATOR: System pressure too low.
- FUEL INJECTORS: Clogged or stuck injector, poor spray pattern.
- FUEL DISTRIBUTOR: Sticking control plunger, mini-filter in fuel inlet banjo bolt clogged or restricted.



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 SYSTEM.