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, electronic-controlled throttle valve system, fuel system and so on. A sudden engine stall could possibly be caused by the poor contact at the connectors.

PROBABLE CAUSES



  • Failed ignition system
  • Failed fuel system
  • Failed air-fuel ratio control system
  • Failed intake air system
  • Contamination around the throttle valve
  • Timing chain in out of place
  • Improper compression pressure
  • Failed variable valve timing control system
  • Failed engine-ECU

DIAGNOSIS PROCEDURE

STEP 1. M.U.T.-III diagnosis code

Q. Is diagnosis code set?
Inspection chart for diagnosis code (Refer to ).
Go to Step 2 .

STEP 2. M.U.T.-III data list

  • Data list reference table (Refer to ).

  1. Item 5: Intake air temperature sensor
  2. Item 6: Engine coolant temperature sensor
  3. Item 8: Manifold absolute pressure sensor
  4. Item 11: Accelerator pedal position sensor (main)
  5. Item 12: Accelerator pedal position sensor (sub)
  6. Item 13: Throttle position sensor (main)
  7. Item 15: Throttle position sensor (sub)
  8. Item 36: V.V.T.phase angle

Q. Are the check results normal?
YES : Go to Step 3 .
Perform the diagnosis code classified check procedure for the sensor that has shown an abnormal data value. Inspection chart for diagnosis code (Refer to ).

STEP 3. Check air intake from inlet hose and inlet manifold.

Q. Is the check result normal?
Go to Step 4 .
Repair.

STEP 4. Check timing mark on the timing chain.

Q. Is the check result normal?
Go to Step 5 .
Align the timing marks.

STEP 5. Check throttle body (throttle valve portion) contamination.

Q. Is the check result normal?
Go to Step 6 .
Throttle body (throttle valve area) cleaning (Refer to ).

STEP 6. M.U.T.-III data list

  • Data list reference table (Refer to ).

  1. Item AC: Oxygen sensor (front)
  2. Item AD: Oxygen sensor (rear)

Q. Are the check results normal?
Go to Step 7 .
Perform the diagnosis code classified check procedure for the sensor that has shown an abnormal data value. Inspection chart for diagnosis code (Refer to ).

STEP 7. Connector check: B-26 engine-ECU connector and B-117 alternator connector

Q. Are the check results normal?
Go to Step 8 .
Repair or replace the connector.

STEP 8. Perform voltage measurement at B-26 engine-ECU connector.

  • Disconnect engine-ECU connector, and connect special tool power plant ECU check harness (MB992110) to measure at connector for inspection.
  • Engine: Idle operation after warm-up
  • Transmission: Neutral
  • Radiator fan: Not operated
  • Voltage between terminal No. 60 and earth.
OK: The voltage increases when the headlamp switch and the rear window defogger switch are turned ON from OFF.

Q. Is the check result normal?
Go to Step 11 .
Go to Step 9 .

STEP 9. Check harness between B-26 (terminal No. 60) engine-ECU connector and B-117 (terminal No. 1) alternator connector.

  • Check output line for open/short circuit and damage.

Q. Is the check result normal?
Go to Step 10 .
Repair the damaged harness wire.

STEP 10. Check the trouble symptom.

Q. Does the trouble symptom persist?
Replace the alternator.
Intermittent malfunction (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions ).

STEP 11. Visual check of ignition spark.

  • Remove the spark plug and install it to the ignition coil.
  • Connect the ignition coil connector.
  • Disconnect all injector connectors.
  • At the engine start, check each spark plug produces a spark.

Q. Is the check result normal?
Go to Step 12 .
Check Inspection Procedure - ignition circuit system (Refer to ).

STEP 12. Check purge control solenoid valve itself.

  • Check purge control solenoid valve itself (Refer to GROUP 17 - Emission Control - Evaporative Emission Control System - Purge Control Solenoid Valve Check ).

Q. Is the check result normal?
Go to Step 13 .
Replace the purge control solenoid valve.

STEP 13. Check injector for spray condition.

  • Injector check (Refer to ).

Q. Is the check result normal?
Go to Step 14 .
Replace the injector.

STEP 14. Check compression pressure.

  • Check the compression pressure (Refer to GROUP 11E - On-vehicle Service - Compression Pressure Check ).

Q. Is the check result normal?
Go to Step 15 .
Repair.

STEP 15. Replace the engine-ECU.

  • After replacing the engine-ECU re-check the trouble symptoms.

Q. Does the trouble symptom persist?
Check for foreign matters (water, diesel fuel, etc.) in fuel and replace if necessary.
Check end.