Hesitation, Sag, Stumble

WARNING: This page is about a different car, the 2007 Isuzu i-370, 2007 GMC Canyon, and 2007 Chevrolet Colorado. 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 . 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 and Engine Controls Schematics .
Sensor/System	NOTE: Refer to Silicon Contamination of Heated Oxygen Sensors Notice . Inspect for proper operation of the manifold absolute pressure (MAP) sensor. Refer to Altitude Versus Barometric Pressure . Verify that the engine coolant temperature (ECT) sensor has not shifted in value. Refer to Temperature Versus Resistance .
Fuel System	Test for incorrect fuel pressure. Refer to Fuel Pump Electrical Circuit Diagnosis . Inspect for a restricted fuel filter. Refer to Fuel Pump Electrical Circuit 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 Diagnosis (w/CH47976) or Fuel Injector Diagnosis (w/J39021 or w/Tech 2) . Inspect for the following that may cause the engine to run rich: NOTE: Refer to Heated Oxygen and Oxygen Sensor Notice . Water intrusion in the heated oxygen sensor (HO2S) connector Purging of a saturated evaporative emission (EVAP) canister Incorrect fuel pressure-Refer to Fuel Pump Electrical Circuit Diagnosis . A leaking fuel pressure regulator-Refer to Fuel Pump Electrical Circuit Diagnosis . Leaking fuel injectors-Refer to Fuel Pump Electrical Circuit 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 . Water intrusion in the HO2S connector An exhaust leak between the HO2S and the engine-Refer to Exhaust Leakage . Vacuum leaks Incorrect fuel pressure-Refer to Fuel Pump Electrical Circuit Diagnosis . Restricted fuel injectors-Refer to Fuel Injector Diagnosis (w/CH47976) or Fuel Injector Diagnosis (w/J39021 or w/Tech 2) . 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	In order to properly inspect the spark plugs or to correct a condition, refer to the following procedures: Ignition System Specifications Spark Plug Replacement Spark Plug Inspection 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 or misaligned spark plug boots. 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 .
Engine Cooling System	Inspect the engine thermostat for proper operation and for correct heat range. Refer to Thermostat Diagnosis .