Hesitation, Sag, Stumble

WARNING: This page is about a different car, the 2004 GMC Sierra and 2004 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.

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 from a stop. May cause the engine to stall if severe enough.
Preliminary	Refer to Important Preliminary Inspections Before Beginning in Symptoms - Engine Controls . Search for bulletins. Inspect the powertrain control module (PCM) 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 for proper operation of the manifold absolute pressure (MAP) sensor. Refer to DTC P0106 . Inspect for proper operation of the throttle position (TP) sensor. Refer to DTC P0121 . Verify that the engine coolant temperature (ECT) sensor has not shifted in value. Refer to Temperature vs Resistance .
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 (Without Special Tool) or Alcohol/Contaminants-in-Fuel Diagnosis (With Special Tool) . Test the fuel injector Refer to Fuel Injector Balance Test with Special Tool , Fuel Injector Balance Test with Tech 2 , or Fuel Injector Coil Test . Inspect for the following 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 heated oxygen sensor (HO2S) connector Purging of a saturated evaporative emission (EVAP) canister Incorrect fuel pressure-Refer to Fuel System Diagnosis . A leaking fuel pressure regulator-Refer to Fuel System Diagnosis . Proper operation of the MAP sensor-Refer to DTC P0106 . Leaking fuel injectors-Refer to Fuel System Diagnosis . 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 and Fuel Injector Balance Test with Tech 2 . Fuel contamination-Refer to Alcohol/Contaminants-in-Fuel Diagnosis (Without Special Tool) or Alcohol/Contaminants-in-Fuel Diagnosis (With Special Tool) . Vacuum hoses that are split, kinked, or improperly connected
Ignition System	In order to properly inspect the spark plugs or to correct a condition, refer to the following procedures: Ignition System Specifications Spark Plug Inspection Spark Plug Replacement Inspect for proper secondary ignition voltage output with J 26792 HEI Spark Tester. An improper spark plug gap will cause a driveability condition. Gap the spark plugs using a wire gage gap tool. If the spark plugs are found to be fouled, determine the cause before replacing the spark plugs. Inspect for damaged spark plug wires. Refer to Spark Plug Wire Inspection . Monitor the Misfire Current Counters while driving the vehicle in the conditions that the symptom occurred. If a misfiring cylinder can be located, use the DTC P0300 table for diagnosis. Refer to DTC P0300 . 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 the water.
Engine Cooling System	Inspect the engine thermostat for proper operation and for correct heat range. Refer to Thermostat Diagnosis in Engine Cooling.