Inspection Procedure 7

Inspection procedure 7: Unstable idle (rough idle, hunting)

COMMENT
- In cases such as the above, the cause is probably the air/fuel mixture. Other systems affecting idle quality include the ignition system and compression.

TROUBLESHOOTING HINTS (The most likely causes for this case:)
- Malfunction of the fuel pump system.
- Malfunction of the ignition system.
- Malfunction of the injector system.
- Poor compression
- Malfunction of the purge control system
- Improper operation of the PCV valve.
- Malfunction of the charging system.
- Vacuum leak.
- Contaminated fuel.
- Malfunction of variable valve timing control (MIVEC) system.
- Malfunction of the ECM.

DIAGNOSIS

Required Special Tools:
- MB991958: Scan Tool (M.U.T.-III Sub Assembly)
- MB991824: V.C.I.
- MB991827: USB Cable
- MB991910: Main Harness A

- MB992110: Power Plant ECU Check Harness

STEP 1. Using scan tool MB991958, read the diagnostic trouble code (DTC)







CAUTION: To prevent damage to scan tool MB991958, always turn the ignition switch is to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991958.

1. Connect scan tool MB991958 to the data link connector.
2. Turn the ignition switch to the "ON" position.
3. Read the DTC.
4. Turn the ignition switch to the "LOCK" (OFF) position.

Q: Is any DTC set?

YES : Refer to Diagnostic Trouble Code Chart. Diagnostic Trouble Code Descriptions

NO : Go to Step 2.

STEP 2. Using scan tool MB991958, check actuator test.

1. Turn the ignition switch to the "ON" position.
2. Check following items in the actuator test. Refer to Actuator Test Reference Table. Actuator Test Reference Table
a. Item 1: Injector.
b. Item 10: Evaporative emission purge solenoid

3. Turn the ignition switch to the "LOCK" (OFF) position.

Q: Are they operating properly?

YES : Go to Step 3.

NO : Repair or replace it. Then confirm that the malfunction symptom is eliminated.

STEP 3. Using scan tool MB991958, check data list.

1. Turn the ignition switch to the "ON" position.
2. Check the following items in the data list. Refer to Data List Reference Table. Datal List Reference Table
a. Item 5: Intake Air Temperature Sensor.
b. Item 6: Engine Coolant Temperature Sensor.
c. Item 10: Mass Airflow Sensor
d. Item 36: Intake V.V.T. phase angle
e. Item 39: Exhaust V.V.T. phase angle
f. Item 76: A/C Switch

3. Turn the ignition switch to the "LOCK" (OFF) position.

Q: Are they operating properly?

YES : Go to Step 4.

NO : Repair or replace it. Then confirm that the malfunction symptom is eliminated.

STEP 4. Check the fuel pressure.

Q: Is the fuel pressure normal?

YES : Go to Step 5.

NO : Repair or replace it. Then confirm that the malfunction symptom is eliminated.

STEP 5. Check the ignition timing.

Q: Is the ignition timing normal?

YES : Go to Step 6.

NO : Check for installed conditions of the timing chain. Then confirm that the malfunction symptom is eliminated.

STEP 6. Measure the voltage at ECM connector B-09 by using check harness special tool MB992110.







1. Disconnect all ECM connectors. Connect the check harness special tool MB992110 between the separated connectors.
2. Start the engine and run at idle.

NOTE: Vehicles for Canada, the headlight, taillight, etc. remain lit even when the lighting switch is in "OFF" position but this is no problem for checks.







3. Measure the voltage between terminal No. 60 and ground.
a. Engine: warming up, idling
b. Radiator fan: stopped
c. Headlight: OFF to ON
d. Stop light: OFF to ON
e. Rear defogger switch: OFF to ON
- Voltage increases

4. Turn the ignition switch to the "LOCK" (OFF) position.

Q: Is the harness measured voltage within the specified range?

YES : Go to Step 7.

NO : Replace the generator. Then confirm that the malfunction symptom is eliminated.

STEP 7. Check the spark plugs.

Q: Are there any abnormalities?

YES : Replace the spark plug. Then confirm that the malfunction symptom is eliminated.

NO : Go to Step 8.

STEP 8. Check the ignition coil.

Q: Are there any abnormalities?

YES : Replace the ignition coil. Then confirm that the malfunction symptom is eliminated.

NO : Go to Step 9.

STEP 9. Check the compression pressure.

Q: Is the compression pressure normal?

YES : Go to Step 10.

NO : Repair it. Then confirm that the malfunction symptom is eliminated.

STEP 10. Check the positive crankcase ventilation system.

Q: Is the positive crankcase ventilation system?

YES : Go to Step 11.

NO : Repair it. Then confirm that the malfunction symptom is eliminated.

STEP 11. Check the purge control system.

Q: Is the purge control system normal?

YES : Check the following items, and repair or replace the defective items.

1. Vacuum leak.
2. Check if fuel is contaminated.
3. Check if the injectors are clogged.

Then confirm that the malfunction symptom is eliminated.

NO : Repair it. Then confirm that the malfunction symptom is eliminated.