GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Isuzu 🢒 2001 🢒 S/T Isuzu - 4WD 🢒 Engine 🢒 Engine Electrical 🢒 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 - Engine Controls .
    • Search for service bulletins.

Fuel System
    • Check system fuel pressure. Refer to Fuel System Diagnosis .
    • Check the fuel composition sensor for accuracy. Perform the Fuel Composition Test and compare the results.
    • Check the fuel filter for being plugged or restricted.
    • Check items which can cause an engine to run rich--Long Term FT significantly in the negative range. Refer to Diagnostic Aids for DTC P0172 .
    • Check items that can cause an engine to run lean--Long Term FT significantly in the positive range. Refer to Diagnostic Aids for DTC P0171 .
    • Check for proper operation of the evaporative emission (EVAP) control system.

Sensor/System
    • If the stalling condition occurs when the A/C is turned ON or when the transmission is put into gear, make sure the PCM recognizes the change in state for the component and the IAC counts change accordingly.
    • Check for proper IAC operation using the scan tool.
    • Check the oxygen sensor (O2S 1). The O2S 1 should respond quickly to different throttle positions. If not, check the O2S 1 for silicon or other contaminants from fuel or the use of improper RTV sealant. The sensors may have a white powdery coating. Silicon contamination causes a high but false O2S 1 signal voltage--rich exhaust indication. The PCM will reduce the amount of fuel delivered to the engine, causing a severe driveability problem.
    • Check for proper operation of the MAP sensor.
    • Check for proper operation of the TP sensor.
    • Check for proper operation of the ECT sensor.

Ignition System
    • Check for proper ignition voltage output with the J 26792 spark tester.
    • Check the spark plugs for the following conditions:
       - Wet or fuel fouled spark plugs
       - Cracks on the spark plugs
       - Wear
       - Improper spark plug gap
       - Burned electrodes or heavy deposits
    • If the spark plugs are fuel or oil fouled, the cause of the fouling must be determined before replacing the spark plugs.
    • Check the ignition control module (ICM) for proper ground connection.
    • Check the ignition coils for cracks or carbon tracking.
    • Check the spark plug wires for the proper resistance and condition.

Engine Mechanical
    • Check engine mechanical for the following:
       - Compression--Refer to Engine Compression Test in Engine Mechanical.
       - Sticking or leaking valves
       - Worn camshaft lobes
       - Valve timing
       - Bent push rods
       - Worn rocker arms
       - Broken valve springs
       - Excessive oil in combustion chamber and leaking valve seals
    • Inspect for the following incorrect basic engine parts:
       - Camshaft
       - Cylinder heads
       - Pistons, etc.
    • Refer to the appropriate diagnostic procedures in Engine Mechanical.

Additional Checks

Check the following components of the exhaust system for possible restrictions:

    • Inspect exhaust system for damaged or collapsed pipes.
    • Inspect mufflers for heat distress or possible internal failure.
    • For possible plugged three-way catalytic converter--Refer to Restricted Exhaust System Check .
    • An engine miss condition can be caused by electromagnetic interference (EMI) on the reference circuit. EMI can usually be detected by monitoring engine RPM with a scan tool. A sudden increase in RPM with little change in actual engine RPM change, indicates EMI is present. If a problem exists, check routing of secondary ignition wires, high voltage components--near ignition control circuits.
    • Check for malfunctioning engine mounts.