Hesitation, Sag, Stumble

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

FUEL SYSTEM
CHECK: Fuel pressure.
CHECK: Throttle Position (TP) sensor Check TP sensor for binding or sticking. Voltage should increase at a steady rate as throttle is moved toward Wide Open Throttle (WOT).
CHECK: MAP sensor response and accuracy. Refer to Diagnostic Charts/C Charts/Manifold Absolute Pressure Output Check MAP Sensor Output Diagnosis
CHECK: Water/Contaminated fuel.
CHECK: Canister purge system for proper operation.
CHECK: Injector driver circuit. Disconnect all injector harness connector(s) at the injector(s). Connect J 34730-2B injector test light or equivalent 12 volts test light between the harness terminals of each injector connector and note light while cranking. If test light fails to blink at any connector, it is a faulty injector drive circuit harness, connector or terminal.
Injector resistance. Measure injector resistance of injector(s). Nominal resistance of each injector should be 1.16 to 1.36 ohms at 20°C (68°F) for TBI and for CMFI the resistance is 1.37 to 1.77 ohms. Resistance will increase slightly at higher temperatures. Perform the injector balance test. Refer to Diagnostic Charts/Chart A-7 Poppet Nozzle Diagnosis of the appropriate engine VIN.
CHECK: Low fuel pressure after a cold start or during moderate or full throttle acceleration. If fuel pressure drops below specification, there is possibly a faulty fuel pump or a restriction in the fuel system.

IGNITION SYSTEM
CHECK: Spark plug wires for being faulty.
CHECK: Spark plugs for being fouled.
CHECK: Open ignition system ground CKT 453 or ignition timing.

ADDITIONAL CHECKS
CHECK: Generator output voltage. Repair if less than 9 or more than 16 volts.
CHECK: EGR valve operation.