GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2005 🢒 STS 🢒 Engine 🢒 Engine Controls - 3.6L (LY7) 🢒 Hesitation, Sag, Stumble

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 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 .
    • Test the fuel injectors. Refer to Fuel Injector Solenoid Coil Test .
    • Test the items that cause an engine to run rich. For a rich condition, refer to DTC P2178 or P2180 and DTC P2188 or P2190 .
    • Test the items that can cause an engine to run lean. For a lean condition, refer to DTC P2177 or P2179 and DTC P2187 or P2189 .

Ignition System
    • 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.
    • 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:
    • If the spark plugs are gas, coolant, or oil fouled, determine the cause before replacing the spark plugs. Refer to the following procedures:
       - Test the items that cause an engine to run rich. For a rich condition, refer to DTC P2178 or P2180 and DTC P2188 or P2190 .
       - For diagnosis of coolant contaminated spark plugs, refer to Loss of Coolant .
       - For diagnosis of oil fouled spark plugs, refer to Oil Consumption Diagnosis .
    • 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 to Thermostat Diagnosis .

Additional
    • Inspect for a condition with the camshaft actuator system. A camshaft actuator that is stuck in the full advance or retard position may cause this symptom. Refer to DTC P0011, P0014, P0021, or P0024 .
    • 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 . Repair the charging system if the generator output voltage is less than 9 volts or more than 16 volts.