Hesitation, Sag, Stumble

WARNING: This page is about a different car, the 2004 Buick Rendezvous. However, it is still accessible from the selected car via links, so may be relevant.

Inspections	Action
DEFINITION: Momentary lack of response as the accelerator is pushed down. This condition can occur at any vehicle speed. This condition is usually more pronounced when first trying to make the vehicle move, as from a stop sign. This condition 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 system grounds for being clean, tight, and in the correct locations. Refer to Power and Grounding Component Views in Wiring Systems and Engine Controls Schematics . Ensure the resistance between the engine control module (ECM) housing and the battery negative cable is less than 0.5 ohms. Verify that the ECM and ECM bracket fasteners are at the correct torque. Remove the air filter element and inspect for restrictions. Refer to Air Cleaner Element Replacement . Inspect the intake air duct and air cleaner outlet resonator for the following conditions: Restrictions Improperly installed hoses Leaks Collapsed hoses
Sensor/System	Test the heated oxygen sensors (HO2S). The HO2S should respond quickly to a change in throttle position. If the HO2S does not respond to different throttle positions, inspect for contamination from fuel, silicon, or incorrect use of RTV sealant. The sensors may have a white powdery coating. The coating causes a low, but false, signal voltage, which gives a rich exhaust indication. The ECM reduces the amount of fuel delivered to the engine, causing a driveability condition. Inspect the mass air flow (MAF) sensor for the correct operation. Refer to DTC P0101 .
Fuel System	Test for incorrect fuel pressure. Refer to Fuel System Diagnosis . Test for a restricted fuel filter. Refer to Fuel System Diagnosis . Test for a contaminated fuel condition. Refer to Alcohol/Contaminants-in-Fuel Diagnosis (w/o Special Tool) or Alcohol/Contaminants-in-Fuel Diagnosis (w/Special Tool) . Test the fuel injectors. Refer to Fuel Injector Coil Test . Test the items that cause an engine to run rich. For a rich condition, refer to DTC P2178 or DTC P2188 . Test the items that can cause an engine to run lean. For a lean condition, refer to DTC P2177 or DTC P2187 .
Ignition System	Test for the correct ignition voltage output with a J 26792 Spark Tester. If you suspect an ignition system condition exists, refer to Electronic Ignition (EI) System Diagnosis . Remove the spark plugs and inspect for the following conditions: Incorrect heat range Wet plugs Cracks Wear Improper gap Burned electrodes Heavy deposits Refer to the following procedures: Spark Plug Replacement Ignition System Specifications Spark Plug Inspection If the spark plugs are gas, coolant or oil fouled, determine the cause before replacing the spark plugs. Refer to the following procedures: For diagnosis of a rich condition, refer to DTC P2178 or DTC P2188 . For diagnosis of coolant contaminated spark plugs, refer to Loss of Coolant in Engine Cooling. For diagnosis of oil fouled spark plugs, refer to Oil Consumption Diagnosis in Engine Mechanical - 3.6L (LY7). Inspect the crankshaft position (CKP) sensor for the correct resistance. The sensor resistance may be out of range after a hot soak. Measure that the resistance remains within 700-1,200 ohms at all temperatures. Inspect the spark plug boots and terminals for burning or micro-arcing, corrosion, and damage to the insulation.
Engine Cooling System	Test the engine thermostat for the correct operation and heat range. Refer toThermostat Diagnosis in Engine Cooling.
Additional	Test for the correct operation of the intake manifold runner control solenoid-Refer to Intake Manifold Runner Control System Diagnosis . Test the generator output voltage-Refer to Symptoms - Engine Electrical in Engine Electrical. Repair the charging system if the generator output voltage is less than 9 volts or more than 16 volts.