Inspection Procedure 8: Unstable Idling (rough idling, hunting), Improper Idling Speed (too high or too low), Engine Stalls During Idling (die out)






COMMENT 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
  • Contamination around the throttle valve
  • Timing chain out of place
  • Compression pressure improper
  • Failed variable valve timing control system
  • Failed engine-ECU

DIAGNOSIS PROCEDURE

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

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

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

  • Refer to Data List Reference Table .

  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?
Go to Step 3 .
Perform the diagnosis code classified check procedure for the sensor that has shown an abnormal data value (Refer to Inspection Chart for Diagnosis Code ).

STEP 3. M.U.T.-III data list

  • Refer to Data List Reference Table .

  1. Item 87: Neutral switch <A/T>

Q. Is the check result normal?
Go to Step 4 .
Carry out checks relating to the system.

STEP 4. Check air intake from inlet hose and inlet manifold.

Q. Is the check result normal?
Go to Step 5 .
Repair.

STEP 5. Check timing marks of timing chain.

Q. Is the check result normal?
Go to Step 6 .
Align timing marks.

STEP 6. Check throttle body (throttle valve portion) contamination.

Q. Is the check result normal?
Go to Step 7 .
Clean throttle body (throttle valve portion) (Refer to ).

STEP 7. M.U.T.-III data list

  • Refer to Data List Reference Table .

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

Q. Are the check results normal?
Go to Step 8 .
Perform the diagnosis code classified check procedure for the sensor that has shown an abnormal data value (Refer to Inspection Chart for Diagnosis Code ).

STEP 8. Connector check: B-08 engine-ECU connector

Q. Is the check result normal?
Go to Step 9 .
Repair or replace the connector.

STEP 9. Perform voltage measurement at B-08 engine-ECU connector.

  • Disconnect engine-ECU connector, and connect special tool power plant ECU check harness (MB992110) to measure at connector for inspection.
  • Engine: Idling after warm-up
  • Transmission: Neutral <M/T> or P range <A/T>
  • Radiator fan: Not operating
  • Voltage between terminal No. 60 and earth.
OK: Voltage increases when the headlamps are extinguished → illuminated.

Q. Is the check result normal?
Go to Step 12 .
Go to Step 10 .

STEP 10. Connector check: B-115 alternator connector

Q. Is the check result normal?
Go to Step 11 .
Repair or replace the connector.

STEP 11. Check harness between B-08 (terminal No. 60) engine-ECU connector and B-115 (terminal No. 1) alternator connector.

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

Q. Is the check result normal?
Replace the alternator.
Repair the damaged harness wire.

STEP 12. 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 13 .
Check ignition circuit system (Refer to Inspection Procedure 23 )

STEP 13. Check purge control solenoid valve itself.

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

Q. Is the check result normal?
Go to Step 14 .
Replace the purge control solenoid valve.

STEP 14. Check injector for spray condition.

  • Check each injector for spray condition (Refer to ).

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

STEP 15. Check compression pressure.

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

Q. Is the check result normal?
Go to Step 16 .
Repair.

STEP 16. Replace the engine-ECU.

  • After replacing the engine-ECU, re-check the trouble symptom.

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