Inspection Procedure 7: Unstable Idling (Rough Idling, Hunting), Improper Idling Speed (Too High or too Low), Engine Stalls during Idling (Die Out)
COMMENTS ON TROUBLE SYMPTOM
- Probable causes can be widely found in the ignition system, air-fuel ratio control system, throttle valve control system, and fuel system, etc. A sudden engine stall is possibly caused by poor contact in the connectors.
PROBABLE CAUSES
- Failed ignition system
- Failed fuel system
- Failed air-fuel ratio control system
- Failed intake and exhaust air system
- Contamination around the throttle valve
- Timing belt in out of place
- Improper compression pressure
- Failed engine-ECU
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STEP 1. M.U.T.-III diagnosis code
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Q.
Is the diagnosis code stored?
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Inspection chart for diagnosis code (Refer to ).
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Go to Step 2.
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STEP 2. M.U.T.-III data list
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- Refer to Data List Reference Table .
- Item 5: Intake air temperature sensor
- Item 6: Engine coolant temperature sensor
- Item 8: Manifold absolute pressure sensor
- Item 10: Air flow sensor
- Item 11: Accelerator pedal position sensor (main)
- Item 12: Accelerator pedal position sensor (sub)
- Item 13: Throttle position sensor (main)
- Item 15: Throttle position sensor (sub)
- Item BB: Barometric pressure sensor
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Q.
Are the check results normal?
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Go to Step 3.
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Perform the diagnosis code classified check procedure for the sensor that has shown an abnormal data value (Refer to Inspection Chart for Diagnosis Code ).
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STEP 3. M.U.T.-III data list
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- Refer to Data List Reference Table .
- Item 83: Power steering fluid pressure switch
- Item 87: Neutral switch
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Q.
Are the check results normal?
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Go to Step 4.
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Perform the diagnosis code classified check procedure for the sensor that has shown an abnormal data value (Refer to Inspection Chart for Diagnosis Code ).
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STEP 4. Check air intake from intake hose and inlet manifold.
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Q.
Is the check result normal?
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Go to Step 5.
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Repair.
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STEP 5. Check timing mark on the timing belt.
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Q.
Is the check result normal?
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Go to Step 6.
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Align the timing marks.
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STEP 6. Check throttle body (throttle valve portion) contamination.
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Q.
Is the check result normal?
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Go to Step 7.
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Clean throttle body (throttle valve portion) (Refer to ).
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STEP 7. M.U.T.-III data list
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- Refer to Data List Reference Table .
- Item AC: Right bank oxygen sensor (front)
- Item AD: Right bank oxygen sensor (rear) <Except Euro 2>
- Item AE: Left bank oxygen sensor (front)
- Item AF: Left bank oxygen sensor (rear) <Except Euro 2>
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Q.
Are the check results normal?
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Go to Step 8.
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Perform the diagnosis code classified check procedure for the sensor that has shown an abnormal data value (Refer to Inspection Chart for Diagnosis Code ).
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STEP 8. Voltage measurement at engine-ECU connector (ALTG line).
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(1)Disconnect engine-ECU connector, and connect special tool power plant ECU check harness (MB992110) to measure at connector for inspection.
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(2)Engine: Idle operation after warm-up
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(4)Radiator fan: Not operated
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(5)Check the voltage between the engine-ECU connector (ALTG line) and body earth. OK: The voltage increases when the headlamp switch and the rear window defogger switch are turned ON from OFF.
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Q.
Is the check result normal?
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Go to Step 11.
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Go to Step 9.
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STEP 9. Check of short to power supply, short to earth, open circuit and damage in ALTG line between engine-ECU connector and alternator connector.
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Q.
Is the check result normal?
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Go to Step 10.
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Repair the connector(s) or wiring harness.
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STEP 10. Check the trouble symptom.
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Q.
Does the trouble symptom persist?
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Replace the alternator.
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Intermittent malfunction (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions ).
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STEP 11. Visual check of ignition spark.
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- Remove the spark plug and install it to the ignition coil.
- Connect the ignition coil connector.
- Remove all injector connectors.
- At the engine start, check each spark plug produces a spark.
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Q.
Is the check result normal?
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Go to Step 12.
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Check Inspection Procedure - ignition circuit system (Refer to ).
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STEP 12. Check purge control solenoid valve itself.
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- Check purge control solenoid valve itself (Refer to GROUP 17 - Emission Control - Evaporative Emission Control System - Purge Control Solenoid Valve Check ).
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Q.
Is the check result normal?
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YES : Go to Step 13.
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Replace the purge control solenoid valve.
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STEP 13. Check injector for spray condition.
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- Check each injector for spray condition (Refer to ).
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Q.
Is the check result normal?
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Go to Step 14.
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Replace the injector.
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STEP 14. Check compression pressure.
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- Check the compression pressure (Refer to GROUP 11C - On-vehicle Service - Compression Pressure Check ).
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Q.
Is the check result normal?
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Go to Step 15.
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Repair.
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STEP 15. Replace the engine-ECU.
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- After the engine-ECU has been replaced, check for the trouble symptom again.
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Q.
Does the trouble symptom persist?
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Check for foreign matters (water, kerosene, etc.) in fuel and replace if necessary.
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Check end.
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