Inspection Procedure 7: 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 ignition system, air-fuel ratio control system, idle speed control system, fuel system, etc. A sudden engine stall is possibly caused by poor connector contact.

PROBABLE CAUSES

Failed ignition system
Failed fuel system
Failed throttle valve control
Failed intake/exhaust system
Throttle valve fouled around
Timing belt out of place
Compression pressure improper
Failed engine-ECU

DIAGNOSIS PROCEDURE

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

Q. 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 .

Item No. 6: Intake air temperature sensor
Item No. 8: Engine coolant temperature sensor
Item No. 11: Accelerator pedal position sensor (main)
Item No. 12: Accelerator pedal position sensor (sub)
Item No. 13: Throttle position sensor (main)
Item No. 14: Throttle position sensor (sub)
Item No. 80: Air flow sensor

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 .

Item No. 79: Barometric pressure sensor

Q. Is the check result normal?

	Go to Step 4 .

	Replace the engine-ECU then perform the variant coding (Refer to GROUP 00 - Precautions Before Service - How to Perform Variant Coding ).

STEP 4. Check throttle body (throttle valve) contamination.

Q. Is the check result normal?

	Go to Step 5 .

	Clean throttle body (throttle valve portion) (Refer to ).

STEP 5. Check for intake of air from gaps in gasket, seals, etc manifold.

Q. Is the check result normal?

	Go to Step 6 .

	Repair for intake of air from gaps in gasket, seals, etc.

STEP 6. Check injector for operating sound.

Check injector for operating sound (Refer to ).

Q. Can operating sound be heard?

	Go to Step 7 .

	Check the injector system of the defective cylinder. (Refer to Code No. P0201: No. 1 Injector System ). (Refer to Code No. P0202: No. 2 Injector System ). (Refer to Code No. P0203: No. 3 Injector System ). (Refer to Code No. P0204: No. 4 Injector System ).

STEP 7. Check timing marks of timing belt.

Q. Is the check result normal?

	Go to Step 8 .

	Align timing marks.

STEP 8. M.U.T.-III data list

Refer to Data List Reference Table .

Item No. 8: Oxygen sensor (front)
Item No. 9: Oxygen sensor (rear)

Q. Are the check result normal?

	Go to Step 9 .

	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 9. Perform voltage measurement at A-34 engine-ECU connector.

Disconnect engine-ECU connector, and connect special tool power plant ECU check harness (MB991987), and then measure the voltage on the check connector.
Engine: Idling after warm-up
Transmission: Neutral
Cooling fan: Not operating
Voltage between terminal No. 54 and earth.

OK: Switching the headlamps to ON from OFF causes the voltage to decrease.

Q. Is the check result normal?

Go to Step 13 .

Go to Step 10 .

STEP 10. Connector check: A-34 engine-ECU connector and A-127 alternator connector

Q. Is the check result normal?

Go to Step 11 .

Repair or replace the connector.

STEP 11. Check harness between A-34 (terminal No. 54) engine-ECU connector and A-127 (terminal No. 4) alternator connector.

Check output line for open/short circuit and damage.

Q. Is the check result normal?

Go to Step 12 .

Repair the damaged harness wire.

STEP 12. Replace the alternator

After alternator is replaced, re-check for trouble symptom.

Q. Does trouble symptom persist?

	Replace the engine-ECU then perform the variant coding (Refer to GROUP 00 - Precautions Before Service - How to Perform Variant Coding ).

	Check end.

STEP 13. Visual check of ignition spark.

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

Q. Is the check result normal?

	Go to Step 14 .

	Check ignition circuit system (Refer to Inspection Procedure 24 ).

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 11E - On-vehicle Service - Compression Pressure Check ).

Q. Is the check result normal?

	Go to Step 16 .

	Repair the compression pressure.

STEP 16. Check purge control solenoid valve itself.

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

Q. Is the check result normal?

	Go to Step 17 .

	Replace the purge control solenoid valve.

STEP 17. M.U.T.-III actuator test

Item No. 5: Fuel pump

OK: Operating sounds of fuel pump can be heard.

Q. Is the check result normal?

	Go to Step 18 .

	Check fuel pump system (Refer to inspection Procedure 22 ).

STEP 18. Replace the engine-ECU.

After engine-ECU is replaced, re-check for trouble symptom.

Q. Does trouble system persist?

	Check for foreign matters (water, kerosene, etc.) in fuel and replace if necessary.

	Check end.