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.