GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 2004 🢒 GTO 🢒 Engine 🢒 Engine Controls - 5.7L 🢒 Rough, Unstable, or Incorrect Idle and Stalling

Checks

Action

DEFINITION : The engine runs unevenly during idle. If the condition is severe, the engine or the vehicle may shake. The engine idle speed may vary in RPM. Either condition may be severe enough to stall the engine.

Preliminary Checks
    • Refer to Important Preliminary Checks Before Starting in Symptoms - Engine Controls .
    • Search for bulletins.
    • Inspect the powertrain control module (PCM) grounds. Ensure that they are clean, tight, and in the proper locations. Refer to Engine Controls Schematics .
    • Remove and Inspect the air filter element for dirt, or for restrictions. Refer to Air Cleaner Element Replacement . Replace the element as necessary.

Fuel System
    • Test the fuel injectors. Refer to Fuel Injector Solenoid Coil Test .
    • 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 .
    • Ensure that each injector harness is connected to the correct injector or cylinder according to the firing order. The firing order is 1-8-7-2-6-5-4-3. Relocate the injector harnesses as necessary.
    • Inspect for conditions that cause an engine to run rich, with a long-term fuel trim near -13 percent. For a rich condition, refer to DTC P0132 or P0152 .
    • Inspect for conditions that can cause an engine to run lean, with a long-term fuel trim near 24 percent. For a lean condition, refer to DTC P0131 or P0151 .

Sensor/System
    • Test the crankcase ventilation valve for proper operation. Place a finger over the inlet hole of the valve end several times. The valve should snap back. If the valve does not snap back, replace the valve.
    • Use a scan tool in order to monitor the KS system for excessive spark retard activity. Refer to Knock Sensor (KS) System Description .

Ignition System
    • Test for proper ignition voltage output with spark tester J 26792 . Refer to Electronic Ignition (EI) System Diagnosis for the procedure.
    • Remove the spark plugs. Inspect for the following conditions:
       - Wet plugs
       - Cracks
       - Wear
       - Improper gap
       - Burned electrodes
       - Heavy deposits
       - Refer to Spark Plug Inspection .
    • An improper spark plug gap causes a driveability condition. Gap the spark plugs using a wire gauge gap tool. Refer to Spark Plug Replacement .
    • Before you replace the spark plugs, determine the cause of the fouling. If the spark plugs are gas-fouled, refer to DTC P0172 or P0175 . If the spark plugs are oil-fouled or coolant-fouled, refer to Oil Consumption Diagnosis in Engine Mechanical-5.7L or Loss of Coolant in Engine Cooling.
    • Inspect the secondary ignition for the following conditions:
       - Inspect the ignition wires arcing to ground.
       - Inspect the ignition wires for proper routing.
    • Wet the secondary ignition system with water from a spray bottle. Wetting the secondary ignition system may help to locate damaged or deteriorated components. When you apply the water, look and listen for arcing or for misfiring.
    •  Inspect for loose ignition coil grounds. Refer to Electronic Ignition (EI) System Diagnosis .

Engine Mechanical
    • Inspect the engine mechanical components for the following conditions:
       - Engine compression. Refer to Engine Compression Test in Engine Mechanical-5.7L.
       - Sticking or leaking valves
       - Worn camshaft lobes
       - The valve timing
       - Bent push rods
       - Worn rocker arms
       - Broken valve springs
       - For specific conditions, refer to Symptoms - Engine Mechanical in Engine Mechanical-5.7L.
       - Inspect for excessive oil in combustion chamber due to leaking valve seals. Refer to Oil Consumption Diagnosis in Engine Mechanical-5.7L.
    • Inspect for incorrect basic engine parts. Inspect the following components:
       - The camshaft
       - The cylinder heads
       - The pistons

Additional Checks
    • Inspect the exhaust system for possible restrictions. Inspect for the following conditions:
       - Inspect the exhaust system for damaged or collapsed pipes. Refer to Restricted Exhaust in Engine Exhaust.
       - Inspect the mufflers for heat distress or for possible internal failure. Refer to Exhaust Leakage in Engine Exhaust.
       - Inspect for possible plugged Three-Way catalytic converters by comparing exhaust system back pressure on each side of engine. Test the back pressure by removing AIR check valves near exhaust manifolds or the Heated Oxygen sensors. Refer to Restricted Exhaust in Engine Exhaust.
    • Electromagnetic interference (EMI) on the reference circuit can cause an engine miss condition. A scan tool can usually detect EMI by monitoring the engine RPM. A sudden increase in the RPM, with little change in the actual engine RPM change indicates that EMI is present. If an EMI condition exists, inspect for high voltage components near the ignition control circuits.
    • Test the PNP switch circuit. Refer to Park/Neutral Position Switch Adjustment in Automatic Transmission-4L60-E.
    • Inspect for faulty engine mounts. Refer to Engine Mount Inspection in Engine Mechanical-5.7L.
    • Inspect the intake and the exhaust manifold passages for casting flash. Refer to Exhaust Manifold Cleaning and Inspection and Intake Manifold Cleaning and Inspection in Engine Mechanical-5.7L.