GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 1998 🢒 Cavalier (CNG) 🢒 Engine 🢒 Engine Controls - 2.2L 🢒 Rough, Unstable, or Incorrect Idle and Stalling

Checks

Action

DEFINITION: The engine runs unevenly at idle. If the condition is severe enough, the engine or 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 Symptoms .
    • Search for service bulletins.

Sensor Checks
    • Inspect the engine coolant temperature (ECT) sensor with the scan tool. Compare the engine coolant temperature with the ambient air temperature on a cold engine. If the coolant temperature reading is more than five degrees greater or less than the ambient air temperature on a cold engine, inspect for high resistance in the ECT sensor circuit. Refer to Temperature vs. Resistance in Engine Controls - 2.2L in the J Platform Service Manual. If the ECT sensor resistance is not within the specification, refer to DTC P0118 ECT Sensor Circuit High Voltage or DTC P0117 ECT Sensor Circuit Low Voltage in Engine Controls - 2.2L in the J Platform Service Manual.
    • Verify the proper operation of the MAP sensor.
    • Verify the proper operation of the TP sensor.
    • Inspect the EGR system for the following conditions:
       - Vacuum leaks in the EGR pipes and the adapter.
       - A stuck open pintle in the EGR valve.

Fuel System Checks
    • Inspect for a rich or lean symptom that causes the condition. Drive the vehicle at the speed of the complaint. Monitoring the oxygen sensors will help to identify the problem.
    • Inspect for fuel in the pressure regulator vacuum hose. If fuel is present, replace the regulator assembly.
    • Inspect the evaporative emission (EVAP) control system. Refer to EVAP Control System Diagnosis in Engine Controls - 2.2L in the J Platform Service Manual.
    • Perform a cylinder compression test. Refer to Engine Compression Test in Engine Mechanical - 2.2L in the J Platform Service Manual.
    • Inspect for leaking fuel injectors. Refer to Fuel Injector Balance Test in Engine Controls - 2.2L in the J Platform Service Manual.
    • Verify the fuel pressure. Refer to Fuel System Diagnosis .
    • Inspect the gas distribution adapter (GDA) for proper installation and connection.

Ignition System Checks

CNG is a gaseous fuel. It requires higher secondary ignition system voltages for the equivalent gasoline operating conditions. If a problem is reported during CNG operation but not during gasoline operation, do not discount the possibility on a CNG-only ignition system failure. Test the system accordingly.

    • Verify the proper ignition output voltage using the J 26792 or the equivalent.
    • Inspect the spark plugs. Remove the spark plugs and inspect them for the following conditions:
       - Wet plugs
       - Cracks on the spark plugs
       - Wear
       - Improper spark plug gap
       - Burned electrodes
       - Heavy deposits
    • Inspect the spark plugs for proper resistance and condition.
    • Inspect the ignition coils for cracks or carbon tracking.
    • Inspect for loose ignition coil connections.
    • Inspect for loose engine control module grounds.
    • Inspect for loose ignition control module grounds.

Engine Mechanical Check
    • Inspect the engine for the following conditions:
       - Broken motor mounts
       - Improper valve timing
       - Low compression
       - Bent pushrods
       - Worn rocker arms
       - Broken or weak valve springs
       - Worn camshaft lobes
    • Refer to Engine Mechanical - 2.2L in the J Platform Service Manual.

Additional Checks

Important: The AF system works on a fumigation principle of fuel induction. It is more sensitive to intake manifold leakage than the gasoline fuel supply system.

    • Inspect for vacuum leaks. Vacuum leaks can cause a higher than normal idle and low idle air control (IAC) count.
    • Verify proper operation of the IAC.
    • Inspect the control module grounds. The grounds should be clean, tight and in their proper locations.
    • Inspect the scan tool in order to determine if the control module is receiving an A/C signal. Refer to A/C Compressor Control Circuit Diagnosis in Engine Controls - 2.2L in the J Platform Service Manual. If a problem exists with the A/C ON, verify the A/C system operation. Refer to A/C System Diagnosis in HVAC Systems with A/C - Automatic in the J Platform Service Manual.
    • Inspect the EGR system for the following conditions:
       - Vacuum leaks in the EGR pipes and the adapter.
       - A stuck open pintle in the EGR valve.
    • Verify that the A/C refrigerant pressure is not too high. Also, inspect for a faulty high pressure switch.
    • Verify proper operation of the crankcase ventilation valve by using these steps:
        1. Place a finger over the inlet hole in the valve end several times.
        2. The valve should snap back.
        3. If the valve does not snap back, replace the valve. Refer to Crankcase Ventilation System Inspection in Engine Controls - 2.2L in the J Platform Service Manual.