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For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2005 🢒 Epica 🢒 Engine 🢒 Engine Controls - 2.5L (LBK) 🢒 Hesitation, Sag, Stumble

Hestitation, Sag, Stumble

Checks

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. This condition may cause the engine to stall in severe conditions.

Preliminary
    • Refer to Important Preliminary Inspections Before Starting in Symptoms - Engine Controls .
    • Search for bulletins.
    • Verify that the engine control module (ECM) grounds are clean, tight, and in the correct locations.

Sensor/System
    • Test for the correct operation of the intake manifold tuning valve (IMTV) system.
    • Test the manifold absolute pressure (MAP) sensor. Refer to DTC P0106 .
    • Use a scan tool in order to monitor the knock sensor (KS) system for excessive spark retard activity. Refer to Knock Sensor (KS) System Description and DTC P0329 or DTC P0334 .

Fuel System
    • Test for incorrect fuel pressure. Refer to Fuel System Diagnosis .
    • Test for a contaminated fuel condition. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
    • Test the fuel injectors. Refer to Fuel Injector Solenoid Coil Test .
    • Test or inspect items that can cause an engine to run lean. For a lean condition, refer to DTC P0171 or P0174 .
    • Test or inspect items that can cause an engine to run rich. For a rich condition, refer to DTC P0172 or P0175 .

Ignition System
    • Wet down the secondary ignition system with water from a spray bottle. Wetting down the secondary ignition system may help locate damaged or deteriorated components. Look/listen for arcing or misfiring as the water is applied.
    • Test the ignition voltage output with the J 26792 Spark Tester. Refer to Electronic Ignition (EI) System Diagnosis .
    • Remove the spark plugs and inspect for the following conditions:
       - Incorrect heat range
       - Wet plugs
       - Cracks
       - Excessive wear
       - Improper gap
       - Burned electrodes
       - Heavy deposits
       - Refer to the following procedures:
    • An incorrect spark plug gap will cause a driveability concern. Refer to Ignition System Specifications .
    • If the spark plugs are fouled by gas, coolant, or oil, determine the cause before replacing the plugs. Refer to the following procedures:
       - For diagnosis of a rich condition, refer to DTC P0172 or P0175 .
       - For diagnosis of coolant or oil fouled spark plugs, refer to Loss of Coolant in Engine Cooling or Symptoms - Engine Mechanical in Engine Mechanical - 2.5L (LBK).
    • Test the crankshaft position (CKP) sensor for the correct resistance. The CKP sensor resistance may be out of range after a hot soak. The resistance should be between 460-620 ohms.
    • Inspect for the correct installation of the ignition coil seals. Incorrect installation may allow water to enter the spark plug area. Inspect for moisture and corrosion.
    • Inspect the ignition coils and the spark plug boots for cracks or carbon tracking.

Engine Cooling System

Test the engine thermostat. Verify that the thermostat is the correct heat range. Refer to Thermostat Diagnosis in Engine Cooling.

Additional Checks

Test the generator. 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.