Hesitation, Sag, Stumble

WARNING: This page is about a different variant/trim than selected.

Inspection/Tests	Action
DEFINITION: Momentary lack of response as the accelerator is pushed down. Can occur at any vehicle speed. Usually more pronounced when first trying to make the vehicle move, as from a stop. May cause the engine to stall if severe enough.
Preliminary	Refer to Important Preliminary Inspections Before Starting in Symptoms - Engine Controls . Search for bulletins. Inspect the engine control module (ECM) grounds for being clean, tight, and in the proper locations. Refer to Power and Grounding Component Views in Wiring Systems, and Engine Controls Schematics .
Sensor/System	NOTE: Refer to Silicon Contamination of Heated Oxygen Sensors Notice in Cautions and Notices. Inspect the heated oxygen sensors (HO2S). The HO2S should respond quickly to different throttle positions. If they do not, inspect the HO2S for silicon or other contaminates from fuel or the use of improper RTV sealant. The sensors may have a white, powdery coating and result in a high but false signal voltage rich exhaust indication. The PCM will then reduce the amount of fuel delivered to the engine causing a severe driveability problem. Inspect the air intake ducts for being collapsed, damaged, loose, improperly installed, or leaking especially between the mass air flow (MAF) sensor and the throttle body. Inspect for proper operation of the manifold absolute pressure (MAP) sensor. Refer to Scan Tool Data Definitions . Verify that the engine coolant temperature (ECT) sensor is not shifted in value. Refer to Temperature Versus Resistance for resistance specifications. Inspect the MAF sensor and intake air system for proper operation. Refer to Scan Tool Data Definitions .
Fuel System	Test for incorrect fuel pressure. Refer to Fuel System Diagnosis . Inspect for a restricted fuel filter. Refer to Fuel System Diagnosis . Inspect for a contaminated fuel condition. Refer to Alcohol/Contaminants-in-Fuel Diagnosis (W/Special Tool) or Alcohol/Contaminants-in-Fuel Diagnosis (W/O Special Tool) . Test the fuel injector Refer to Fuel Injector Balance Test with Special Tool or Fuel Injector Solenoid Coil Test . Inspect for the following conditions that may cause the engine to run rich: NOTE: Refer to Heated Oxygen and Oxygen Sensor Notice in Cautions and Notices. Water intrusion in the HO2S connector Engine oil contaminated by fuel An evaporative emission (EVAP) canister purge condition Incorrect fuel pressure-Refer to Fuel System Diagnosis . Leaking fuel injectors-Refer to Fuel System Diagnosis . Inspect for proper operation of the MAP sensor. Refer to Scan Tool Data Definitions . Inspect for proper operation of the MAF sensor. Refer to Scan Tool Data Definitions . Vacuum hoses that are split, kinked, or improperly connected An air intake duct that is collapsed or restricted An air filter that is dirty or restricted-Refer to Air Cleaner Element Replacement . Inspect for the following conditions that may cause the engine to run lean: NOTE: Refer to Heated Oxygen and Oxygen Sensor Notice in Cautions and Notices. Water intrusion in the HO2S connector An exhaust leak between the HO2S and the engine-Refer to Exhaust Leakage in Engine Exhaust. Vacuum leaks Incorrect fuel pressure-Refer to Fuel System Diagnosis . Restricted fuel injectors-Refer to Fuel Injector Balance Test with Special Tool . Inspect for proper operation of the MAF sensor. Refer to Scan Tool Data Definitions . Fuel contamination-Refer to Alcohol/Contaminants-in-Fuel Diagnosis (W/Special Tool) or Alcohol/Contaminants-in-Fuel Diagnosis (W/O Special Tool) . Vacuum hoses that are split, kinked, or improperly connected
Ignition System	Soak the secondary ignition system with water from a spray bottle. Soaking the secondary ignition system may help locate damaged or deteriorated components. Look and listen for arcing or misfiring as you apply water. Monitor the Misfire Current Counters while driving the vehicle in the conditions that the misfire occurred. Test for proper ignition voltage output with the J 26792 Spark Tester. Refer to Electronic Ignition (EI) System Diagnosis . Remove the spark plugs and check for the following conditions: Correct heat range Wet plugs Cracks Wear Improper gap Burned electrodes Heavy deposits Refer to Spark Plug Inspection . An improper spark plug gap will cause a driveability problem. Gap the spark plugs using a wire gage gap tool. Refer to Ignition System Specifications and Spark Plug Replacement . Determine the cause of the fouling before replacing the spark plugs. Inspect the spark plug boots for signs of arcing, cracks, carbon tracking, or damage. Inspect for loose ignition coil ground. Refer to Power and Grounding Component Views in Wiring Systems.
Engine Cooling System	Inspect the engine thermostat for proper operation and for correct heat range. Refer to Thermostat Diagnosis in Engine Cooling.
Engine Mechanical	Inspect for excessive crankshaft endplay that will cause the crankshaft position (CKP) sensor reluctor wheel to move out of alignment with the CKP sensor. Refer to Crankshaft and Bearing Cleaning and Inspection in Engine Mechanical. This could result in any of the following conditions: A no start A start and stall Erratic performance
Additional Inspections	Inspect the generator output voltage. Refer to Charging System Test in Engine Electrical.