Hesitation/Sag/Stumble

SYMPTOM DESCRIPTION:

Momentary lack of response when the accelerator is pushed down. Can occur at any speed. Usually most severe from a stop or initial take off. Engine may stall if condition is bad enough.

SYSTEM OR COMPONENT TO CHECK

COMPUTER INPUTS/OUTPUTS
CHECK:
THROTTLE VALVE SWITCH: Check for binding, sticking, or improper adjustment.
AIR MASS METER: Meter or wiring defective
FUEL INJECTION CONTROL UNIT: Check for correct control unit, defective unit or wiring
IGNITION CONTROL UNIT: Control unit or wiring defective
CRANKSHAFT POSITION/SPEED SENSOR: Damaged or incorrectly positioned sensor,
OXYGEN SENSOR: Damaged or defective oxygen sensor.

FUEL
CHECK:
FUEL PRESSURE: Check for insufficient fuel pressure or volume.
FUEL INJECTORS: Clogged or stuck injector, poor spray pattern
FUEL QUALITY: Contaminated, or wrong octane

IGNITION
CHECK: Faulty spark plug wires. Fouled spark plugs.

EMISSIONS
CHECK:
EVAPORATIVE SYSTEM: Cannister purge system operation.

NOTE: Refer to EMISSION CONTROLS for testing procedures.





ENGINE
CHECK:
CHARGING VOLTAGE: Test battery condition,
and alternator output.
VACUUM OR CRANKCASE AIR LEAKS: Check
intake manifold, dip stick tube, engine radial seals.