Hesitation, Sag, Stumble

Definition: Momentary lack of response as the accelerator is pushed down. Can occur at all car speeds. Usually most severe when first trying to make the car move, as from a stop sign. May cause engine to stall if severe enough.


PRELIMINARY CHECKS

- Perform the careful visual/physical checks as described at start of "Symptoms,".


SENSORS

- CHECK: Throttle position sensor for binding or sticking. Voltage should increase at a steady rate as throttle is moved toward Wide Open Throttle.

- CHECK: Manifold absolute pressure sensor- use CHART C-1D.


FUEL SYSTEM

- CHECK: Fuel pressure, use CHART A-7.

- CHECK: Fuel injectors are correct for vehicle.

- CHECK: Contaminated fuel.

- CHECK: Evaporative emission canister purge system for proper operation. Refer to Evaporative Emission System.


IGNITION SYSTEM

- CHECK: Spark plugs for being fouled, or for faulty secondary wiring.

- CHECK: Ignition timing, using a "Scan tool".

- CHECK: Ignition system ground.


ADDITIONAL CHECKS

- CHECK: Exhaust gas recirculation operation, use CHART C-7.

- CHECK: Engine thermostat functioning correctly and proper heat range.

- CHECK: Generator output voltage. Repair if less than 9 or more than 16 volts.