Hesitation, Sag, Stumble

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,

IMPORTANT PRELIMINARY CHECKS
Before using this section you should have performed the "On-Board Diagnostic System Check" - Powertrain/On-Board Diagnostic System Check and determined that:
1. The control module and MIL (Service Engine Soon) are operating correctly.
2. There are no diagnostic trouble codes stored, or there is a diagnostic code but no MIL (Service Engine Soon).
^ Several of the following symptom procedures call for a careful visual/physical check. The importance of visual/physical checks cannot be over stressed. because they can lead to correcting a problem without further checks and can save valuable time.

VISUAL / PHYSICAL CHECK
This check should include:
^ Control module grounds for being clean, tight, and in their proper location.
^ Vacuum hoses for splits, kinks and proper connections, as shown on "Vehicle Emission Control Information" label Check thoroughly for any type of leak or restriction.
^ Air leaks at all mounting areas of the intake manifold sealing surfaces.
^ Ignition wires for cracking, hardness, proper routing, or carbon tracking.
^ Wiring for proper connections, pinches, and cuts.
^ The following symptom charts contain groups of possible causes for each symptom and cover several engines. These procedures are not necessarily meant to be done in consecutive order. If Tech 1 scan tool readings do not indicate the problems, then proceed in a logical order, easiest to check or most likely cause first. To determine if a particular system or component is used on a specific vehicle, refer to the "Electronic/Powertrain Control Module (ECM/PCM)" Wiring Diagrams for application. Electronic/Powertrain Control Module (ECM/PCM)

FUEL SYSTEM
^ CHECK: Fuel pressure. 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 "Manifold Absolute Pressure (MAP) Output Check". MAP Sensor Output Diagnosis
^ CHECK: Water/contaminated fuel. Component Tests and General Diagnostics
^ CHECK: Canister purge system for proper operation. Canister Purge Solenoid

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: Service Bulletins for PROM updates.
^ CHECK: Generator output voltage. Repair if less than 9.0 or more than 16.0 volts.
^ CHECK: EGR valve operation. Testing and Inspection