Inspection Procedure 8
INSPECTION PROCEDURE 8: Unstable Idle (Rough Idle, Hunting)COMMENT
- In cases such as the above, the cause is probably the air/fuel mixture or idle air control motor. Other systems affecting idle quality include the ignition system and compression.
TROUBLESHOOTING HINTS (The most likely causes for this case:)
- Malfunction of the ignition system.
- Malfunction of air/fuel ratio control system.
- Malfunction of the IAC system.
- Malfunction of the evaporative emission purge solenoid system.
- Poor compression pressure.
- Vacuum leak
- Malfunction of the EGR vacuum regulator solenoid valve system.
DIAGNOSIS
Required Special Tools:
- MB991958: Scan Tool (M.U.T.-III Sub Assembly)
- MB991824: V.C.I.
- MB991827: USB Cable
- MB991911: Main Harness B
STEP 1. Check if the battery terminal was disconnected.
Q: Has the battery terminal been disconnected lately?
YES: Start the engine and let it run at idle for approximate 10 minutes after engine warm up. Then, if a malfunction occurs, go to Step 2.
NO: Go to Step 2.
STEP 2. 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 DTC set?
YES: Refer to, Diagnostic Trouble Code Chart. Diagnostic Trouble Code Descriptions
NO: Go to Step 3.
STEP 3. Check the engine idling state.
Q: Is it hunting remarkably?
YES: Go to Step 4.
NO: Go to Step 5.
STEP 4. Check the following items.
1. Carry out the following cleaning.
a. Clean the throttle valve area (Refer to On-vehicle Service - Throttle Body Cleaning).
2. After cleaning, confirm that the malfunction symptom is eliminated.
Q: Is the malfunction symptom resolved?
YES: The check is completed.
NO: Check the following items, and repair or replace the defective items.
a. Broken intake manifold gasket.
b. Broken air intake hose.
c. Broken vacuum hose.
d. Positive crankcase ventilation valve does not operate.
Then confirm that the malfunction symptom is eliminated.
STEP 5. Check the idle air control (IAC) motor operation sound.
1. Check that the engine coolant temperature is 20 degrees C (68 degrees F) or below.
NOTE: Disconnecting the engine coolant temperature sensor connector and connecting the harness side of the connector to another engine coolant temperature sensor that is at 20 degrees C (68 degrees F) or below is also acceptable.
2. Check the operation sound of the IAC motor can be heard after the ignition is switched to the "ON" position (but without starting the engine).
- An operation sound is heard.
3. Turn the ignition switch to the "LOCK" (OFF) position.
Q: Did you hear the operation sound?
YES: Go to Step 6.
NO: Refer to, DTC P0506 - Idle Control System RPM Lower Than Expected P0506, DTC P0507 - Idle Control System RPM Higher Than Expected P0507.
STEP 6. Using scan tool MB991958, check actuator test items 01, 02, 03, 04: Injector.
CAUTION: To prevent damage to scan tool MB991958, always turn the ignition switch 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. Check following items in the actuator test. Refer to, Actuator Test Reference Table. Actuator Test Reference Table
a. Items 01, 02, 03, 04: Injector.
4. Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is the actuator operating properly?
YES: Go to Step 7.
NO: Refer to, DTC P0201, P0202, P0203, P0204 - Injector Circuit P0201.
STEP 7. 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. Data List Reference Table & Normal Scan Data Values
a. Item 13: Intake Air Temperature Sensor.
b. Item 25: Barometric Pressure Sensor.
c. Item 21: Engine Coolant Temperature Sensor.
d. Item 59: Heated Oxygen Sensor (rear).
e. Item 11: Heated Oxygen Sensor (front).
f. Item 27: Power Steering Pressure Switch.
g. Item 28: A/C Switch.
3. Turn the ignition switch to the "LOCK" (OFF) position.
Q: Are they operating properly?
YES: Go to Step 8.
NO: Repair or replace it. Then confirm that the malfunction symptom is eliminated.
STEP 8. Using scan tool MB991958, check actuator test.
1. Turn the ignition switch to the "ON" position.
2. Check the following items in the actuator test. Refer to, Actuator Test Reference Table. Actuator Test Reference Table
a. Item 08: Evaporative Emission Purge Solenoid.
b. Item 10: EGR Vacuum Regulator Solenoid Valve.
3. Turn the ignition switch to the "LOCK" (OFF) position.
Q: Are they operating properly?
YES: Go to Step 9.
NO: Repair or replace it. Then confirm that the malfunction symptom is eliminated.
STEP 9. 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. Data List Reference Table & Normal Scan Data Values
a. Item 45: Idle Air Control Motor Position.
3. Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is the actuator operating properly?
YES: Go to Step 10.
NO: Adjust the basic idle speed. After adjusting, confirm.
STEP 10. Using scan tool MB991958, check data list.
1. Turn the ignition switch to the "ON" position.
2. Check the following items of the data list. Refer to, Data List Reference Table. Data List Reference Table & Normal Scan Data Values
a. Item 11: Heated Oxygen Sensor (front).
- Voltage should fluctuate between 0 - 0.4 volt and 0.6 - 1.0 volt while idling after the engine has been warmed.
3. Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is the sensor operating properly?
YES: Go to Step 12.
NO: Go to Step 11.
STEP 11. Check the fuel pressure.
Refer to On-vehicle Service Fuel Pressure Test. Testing and Inspection
Q: Is the fuel pressure normal?
YES: a. Check the following items, and repair or replace the defective items.
a. Vacuum leak.
- Broken intake manifold gasket.
- Broken air intake hose.
- Broken vacuum hose.
- Positive crankcase ventilation valve does not operate.
b. Injector clogged.
Then confirm that the malfunction symptom is eliminated.
NO: Repair or replace it. Then confirm that the malfunction symptom is eliminated.
STEP 12. Check the ignition timing.
Refer to On-vehicle Service - Ignition Timing Check in Ignition Timing.
Q: Is the ignition timing normal?
YES: Check the following items, and repair or replace the defective items.
a. Check the ignition coil, spark plugs, spark plug cables.
b. Check the purge control system.
c. Check compression pressure.
d. Check if the foreign materials (water, kerosene, etc.) got into fuel.
e. Check the EGR control system.
Then confirm that the malfunction symptom is eliminated.
NO: Check that the crankshaft position sensor and timing belt cover are in the correct position. Then confirm that the malfunction symptom is eliminated.