GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2000 🢒 Sonoma Pickup - 4WD 🢒 Engine 🢒 Engine Controls - 2.2L 🢒 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 .
    • Search for service bulletins.

Fuel System
    • Test for proper fuel pressure. Refer to Fuel System Diagnosis .
    • Test the fuel injectors. Refer to Sequential Multiport Fuel Injector Balance Test .
    • Test for contaminated fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
    • Test the fuel filter for being plugged or restricted.
    • Inspect items which can cause an engine to run rich (Long Term FT significantly in the negative range). Refer to Diagnostic Aids for DTC P0172 Fuel Trim System Rich .
    • Inspect items that can cause an engine to run lean (Long Term FT significantly in the positive range). Refer to Diagnostic Aids for DTC P0171 Fuel Trim System Lean .
    • Test for proper operation of the evaporative emission (EVAP) control system.
    • Inspect for fuel in the fuel pressure regulator vacuum hose.

Sensor/System
    • The O2S 1 should respond quickly to different throttle positions. If not, inspect 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. Refer to oxygen sensor in Information Sensors/Switches Description .
    • Test for proper operation of the following sensors:
       - MAP
       - TP
       - ECT
       - Check for proper operation at the IAC valve,

Ignition System
    • Test for proper ignition voltage output with a J 26792 Spark Tester or equivalent.
    • Inspect the spark plugs for the following conditions:
       - Wet or fuel fouled
       - Cracks
       - Wear
       - Improper gap
       - Burnt 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.
    • Inspect the ignition control module (ICM) for proper ground connection.
    • Inspect the ignition coils for cracks or carbon tracking.
    • Test/inspect the spark plug wires for the proper resistance and condition.

Engine Mechanical
    • Inspect engine mechanical for the following conditions:
       - Compression, refer to Engine Compression Test in Engine Mechanical
       - Sticking or leaking valves, refer to Valve Train Diagnosis in Engine Mechanical
       - Worn camshaft lobes, refer to Camshaft and Bearings Cleaning and Inspection in Engine Mechanical
       - Valve timing, refer to Camshaft Timing Chain and Sprocket Cleaning and Inspection in Engine Mechanical
       - Bent push rods, refer to Valve Train Diagnosis in Engine Mechanical
       - Worn rocker arms, refer to Valve Train Diagnosis in Engine Mechanical
       - Broken valve springs, refer to Valve Train Diagnosis in Engine Mechanical
       - Excessive oil in combustion chamber -- Leaking valve seals, refer to Oil Consumption Diagnosis in Engine Mechanical
    • For incorrect basic engine parts. Inspect the following:
       - Camshaft
       - Cylinder heads
       - Pistons, etc.

Additional Checks
    • Inspect the exhaust system for the following conditions:
       - Damaged or collapsed pipes
       - Mufflers for heat distress or possible internal failure
       - 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, inspect routing of secondary ignition wires, high voltage components (near ignition control circuits).
    • Inspect for malfunctioning motor mounts. Refer to Engine Mount Inspection in Engine Mechanical.