GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 1998 🢒 Firebird 🢒 Engine 🢒 Engine Controls - 5.7L 🢒 Rough, Unstable, or Incorrect Idle and Stalling

Checks

Action

Definition: Engine runs unevenly at idle. If severe, the engine or vehicle may shake. Engine idle speed may vary in RPM. Either condition may be severe enough to stall the engine.

Preliminary Checks
    • Refer to Symptoms , Important Preliminary Checks Before Starting.
    • Search for bulletins.
    • Verify the PCM grounds for being clean, tight and in the proper locations. Refer to Ground Distribution Schematics in Wiring Systems.
    • Remove and inspect the air filter element for dirt, or for being restricted. Refer to Air Cleaner Element Replacement . Replace as necessary.

Fuel System
    • Perform the injector balance test. Refer to Fuel Injector Balance Test for procedure.
    • Test for a low fuel pressure condition. 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 .
    • Verify that each injector harness is connected to the correct injector/cylinder according to the firing order (firing order: 1-8-7-2-6-5-4-3). Relocate injector harnesses as necessary.
    • Test for injectors that are shorted internally. Compare the injector resistance. Injector resistance should be within one ohm of each other. Refer to Fuel Injector Solenoid Coil Test - Engine Coolant Temperature Between 10-35 Degrees C (50-95 Degrees F) .
    • Inspect items that cause an engine to run rich (long term fuel trim near -13%). For a rich condition, refer to DTC P0132 HO2S Circuit High Voltage Bank 1 Sensor 1 and DTC P0152 HO2S Circuit High Voltage Bank 2 Sensor 1 .
    • Inspect items that can cause an engine to run lean (long term fuel trim near 23%). For a Lean condition, refer to DTC P0131 HO2S Circuit Low Voltage Bank 1 Sensor 1 and DTC P0151 HO2S Circuit Low Voltage Bank 2 Sensor 1 .

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

Ignition System
    • Test for proper ignition voltage output with spark tester J 26792 . Refer to Electronic Ignition (EI) System Diagnosis for procedure.
    • Remove spark plugs and inspect for the following:
       - Wet plugs
       - Cracks
       - Wear
       - Improper gap
       - Burned electrodes
       - Heavy deposits
    • An improper spark plug gap will cause a driveability condition. Do the spark plug gapping using a wire gauge gap tool (J 41319). Refer to Spark Plug Replacement in Engine Electrical. Determine the cause of the fouling before replacing the spark plugs. Refer to DTC P0172 Fuel Trim System Rich Bank 1 and DTC P0175 Fuel Trim System Rich Bank 2 for diagnosis of the rich condition or to Oil Consumption Diagnosis in Engine Mechanical 5.7L for diagnosis of the oil fouling condition.
    • Visually/Physically inspect Secondary ignition for the following:
       - Ignition wires for cross firing
       - Ignition wires arcing to ground
       - Ignition wires for proper routing
    • 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 you apply water.
    •  Inspect for loose ignition coil grounds. Refer to Electronic Ignition (EI) System Diagnosis .

Engine Mechanical
    • Inspect engine mechanical for the following:
       - Test compression. Refer to Engine Compression Test in Engine Mechanical 5.7L.
       - Sticking or leaking valves. Refer to Valve Train Diagnosis in Engine Mechanical 5.7L.
       - Worn camshaft lobe(s). Refer to Engine Compression Test in Engine Mechanical 5.7L.
       - Valve timing. Refer to Engine Compression Test in Engine Mechanical 5.7L.
       - Bent push rods. Refer to Engine Compression Test in Engine Mechanical 5.7L.
       - Worn rocker arms. Refer to Engine Compression Test in Engine Mechanical 5.7L.
       - Broken valve springs. Refer to Engine Compression Test in Engine Mechanical 5.7L.
       - Excessive oil in combustion chamber-Leaking valve seals. Refer to Oil Consumption Diagnosis in Engine Mechanical 5.7L.
    • For incorrect basic engine parts. Inspect the following:
       - Camshaft
       - Cylinder heads
       - Pistons, etc.

Additional Checks
    • Inspect the exhaust system for possible restrictions. Inspect for the following:
       - Inspect the exhaust system for damaged or collapsed pipes.
       - Inspect the exhaust manifold for a collapsed inner wall.
       - Inspect the mufflers for heat distress or possible internal failure.
       - Inspect for possible plugged Three-Way catalytic converters. Refer to Restricted Exhaust System Check 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 RPM with little change in actual engine RPM change, this indicates that EMI is present. If a condition exists, inspect routing of secondary ignition wires or high voltage components near ignition control circuits.
    • Test the PNP switch circuit. Refer to Park/Neutral Position Switch Diagnosis .
    • Inspect for faulty motor mounts.
    • Inspect the intake manifold and the exhaust manifold passages for casting flash. Refer to Intake Manifold Clean and Inspect and Exhaust Manifold Cleaning and Inspection in Engine Mechanical 5.7L.