GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2001 🢒 Corvette 🢒 Engine 🢒 Engine Electrical 🢒 Rough, Unstable, or Incorrect Idle and Stalling

Checks

Action

DEFINITION: The engine runs unevenly at idle. If severe, the engine or the vehicle may shake. 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 for being 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 as necessary.

Fuel System
    • Test the fuel injectors. Refer to Fuel Injector Solenoid Coil Test .
    • Test for incorrect fuel pressure. Refer to Fuel Injector Solenoid Coil Test .
    • Test for a restricted fuel filter. Refer to Fuel Injector Solenoid Coil Test .
    • Test for a contaminated fuel condition. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
    • Inspect that each injector harness is connected to the correct injector and the 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 items which can cause an engine to run rich, having the long term fuel trim near -13 percent. For a rich condition, refer to DTC P0131 or P0151 and DTC P0132 or P0152 .
    • Inspect for items that can cause an engine to run lean, having the long term fuel trim near 23 percent. For a lean condition, refer to DTC P0131 or P0151 and DTC P0132 or P0152 .

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 not, replace the valve.
    • 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 .

Ignition System
    • Test for proper ignition voltage output withJ 26792 Spark Tester. Refer to Electronic Ignition (EI) System Diagnosis for the proper procedure.
    • Remove the spark plugs and inspect the plugs for the following conditions:
       - The correct heat range
       - Wet plugs
       - Cracks
       - Wear
       - Improper gap
       - Burned electrodes
       - Heavy deposits
    • In order to properly inspect the spark plugs or to correct a condition, refer to the following procedures:
       -  Spark Plug Inspection
       -  Spark Plug Replacement
    • An improper spark plug gap causes a driveability concern. Gap the spark plugs using a wire gauge gap tool. Refer to Spark Plug Replacement .
    • Determine the cause of the fouling before replacing the spark plugs if the spark plugs are gas, coolant or oil fouled. Refer to DTC P0172 or P0175 for diagnosis of the rich condition. Refer to Spark Plug Inspection for diagnosis of coolant or oil fouled spark plugs.
    • Visually and physically inspect the secondary ignition for the following conditions:
       - The ignition wires arcing to ground--Refer to Spark Plug Wire Inspection
       - The ignition wires for proper routing--Refer to Spark Plug Wire Replacement .
       - The ignition coils for cracks or carbon tracking
    • Wet the secondary ignition system with water from a spray bottle. Wetting the secondary ignition system may help to locate damaged or deteriorated components. Look and listen for arcing or misfiring as you apply the water.
    • Inspect for loose ignition coil grounds. Refer to Electronic Ignition (EI) System Diagnosis .

Engine Mechanical
    • Inspect the engine mechanical components or the following conditions:
       - Test the compression
       - Sticking or leaking valves
       - Worn camshaft lobes
       - Valve timing
       - Bent push rods
       - Worn rocker arms
       - Broken valve springs
       - Excess oil in the combustion chamber-Inspect for leaking valve seals
    • For more information, refer to one or more of the following procedures in Engine Mechanical-5.7L:
       -  Engine Compression Test
       -  Symptoms - Engine Mechanical
       -  Oil Consumption Diagnosis
    • Inspect for incorrect engine parts, such as the following basic components:
       - The camshaft
       - The cylinder heads
       - The pistons

Additional Checks
    • Inspect the following exhaust system components for possible restrictions:
       - The exhaust system for physical damage
       - The exhaust manifold for a collapsed inner wall
       - The mufflers for heat distress or possible internal failure
       - The 3-way catalytic converters for possible plugged pipes by comparing the exhaust system back pressure on each side of engine
    • For more information, refer to the following procedures in Engine Exhaust:
       -  Exhaust Leakage
       -  Restricted 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 the actual engine RPM change indicates that EMI is present. If a condition exists, inspect for any high voltage components near the ignition control circuits.
    • Inspect for faulty engine mounts. Refer to Engine Mount Replacement - Left Side or Engine Mount Replacement - Right Side in Engine Mechanical-5.7L for inspection of the mounts.
    • Inspect the intake manifold and the exhaust manifold passages for casting flash. Refer to Intake Manifold Cleaning and Inspection or Exhaust Manifold Cleaning and Inspection in Engine Mechanical-5.7L.