GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Saturn 🢒 2004 🢒 VUE - AWD 🢒 Engine 🢒 Engine Controls - 3.5L (L66) 🢒 Rough, Unstable, or Incorrect Idle and Stalling

Rough, Unstable, or Incorrect Idle, Stalling

Checks

Action

DEFINITION: The engine runs unevenly at idle. If 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. The engine idles at an incorrect speed.

Preliminary Check
    • Refer to Symptoms - Engine Controls .

Sensor Checks
    • Inspect the engine coolant temperature (ECT) sensor. A fixed or inaccurate ECT sensor reading can cause the engine idle to surge or race. Using the scan tool, compare the ECT with the ambient air temperature on a cold engine. If the engine coolant is 5°C (9°F) more than or 5°C (9°F) less than the ambient air temperature, inspect the resistance of the coolant sensor. Refer to Temperature Versus Resistance - Engine Coolant Temperature Sensor . If the ECT is significantly less than the ambient air temperature, inspect the coolant sensor electrical circuit for high resistance.
    • Inspect the throttle actuator control (TAC) system for correct operation.

Fuel System Checks
    • Inspect the operation of the fuel system for rich or lean condition. Operate the vehicle under the conditions that caused the concern. Monitor the Fuel Trim parameter on a scan tool in order to identify the problem.
       - Lean--The Long Term Fuel Trim will be more than 17 percent. Refer to Diagnostic Aids in DTC P0171 or P0174 .
       - Rich--The Long Term Fuel Trim will be more than -15 percent. Refer to Diagnostic Aids in DTC P0172 or P0175
    • Test the fuel pressure while the condition exists. Refer to Fuel System Diagnosis .
    • Inspect the evaporative emission (EVAP) control system for a saturated EVAP canister.
    • Test the fuel injectors for leaking. Refer to Fuel Injector Balance Test with Tech 2 .

Ignition System Checks
    • Test for the proper secondary voltage output with a J 26792 Spark Tester.
    • Inspect the spark plugs for correct operation and good ignition system performance. Refer to Spark Plug Inspection .
    • Inspect the ignition coil boots for damage.

Engine Mechanical Check
    • Inspect for the following engine mechanical conditions:
       - Any faulty hydraulic lifter assemblies
       - Any broken or weak valve springs
       - A low compression
       - An incorrect valve timing
       - Any sticking or leaking valves
       - An incorrect or worn camshaft
    • Refer to the Symptoms - Engine Mechanical in Engine Mechanical - 3.5L.

Additional Checks
    • Inspect for vacuum leaks. Vacuum leaks can cause a higher than normal idle speed.
    • Verify the PCM grounds are clean, tight, and in the proper locations. Refer to Engine Controls Schematics .
    • An incorrect TP learned value can cause a rough or incorrect idle speed concern and needs to be reset. Before resetting the TP learned value, inspect for excess deposits in the throttle body and clean as necessary. Refer to Throttle Body Inspection and Cleaning and Scan Tool Output Controls .
    • Check the scan tool to determine if the PCM is receiving an A/C signal. The idle speed should be increased with the A/C ON.
    • Inspect the battery cables and the ground straps. They should be clean and secure.
    • Inspect the A/C refrigerant pressure for being too high or for a faulty high pressure switch. Refer to Air Conditioning (A/C) System Performance Test in Heating, Ventilation, and Air Conditioning.
    • The engine will run rough and the engine can stall if the rocker arm oil control solenoid. stuck ON. Refer to DTC P2647 .
    • Inspect the positive crankcase ventilation (PCV) valve for correct operation and the correct part. Refer to Crankcase Ventilation System Inspection/Diagnosis in Engine Mechanical - 3.5L.
    • Inspect for the correct operation of the exhaust gas recirculation (EGR) valve. An EGR valve that leaks can cause a rough idle condition.
    • Verify that the PCM is increasing the idle speed when the P/S system pressure is increased on turns.
    • Inspect for broken or worn motor and transmission mounts.