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 electronic control throttle valve system. 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 electronic control throttle valve system.
- Malfunction of the evaporative emission purge solenoid system.
- Malfunction of the EGR valve.
- Poor compression pressure.
- Vacuum leak.
DIAGNOSIS
Required Special Tools:
- MB991958: Scan Tool (M.U.T.-III Sub Assembly)
- MB991824: V.C.I.
- MB991827: USB Cable
- MB991910: Main Harness A
STEP 1. Check if the battery terminal is 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 the DTC set?
YES : Refer to MFI, Diagnostic Trouble Code Chart. Diagnostic Trouble Code Descriptions
NO : Go to Step 3.
STEP 3. Check the engine idling state.
Q: Is it noticeably hunting?
YES : Go to Step 4.
NO : Go to Step 5.
STEP 4. Check the following items.
1. Carry out the following cleaning.
a. Refer to MFI, On-vehicle Service -Clean the throttle valve area.
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. Using scan tool MB991958, check actuator test items 1, 2, 3, 4: 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 MFI, Actuator Test Reference Table. Actuator Test Reference Table
a. Item 1, 2, 3, 4: Injector.
4. Turn the ignition switch to the "LOCK" (OFF) position.
Q: Are they operating properly?
YES : Go to Step 6.
NO : Refer to DTC P0201 -Injector Circuit-cylinder 1, P0201 DTC P0202 -Injector Circuit-cylinder 2, P0202 DTC P0203 -Injector Circuit-cylinder 3, P0203 DTC P0204 -Injector Circuit-cylinder 4. P0204
STEP 6. 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 MFI, Data List Reference Table. Datal List Reference Table
a. Item 5: Intake Air Temperature Sensor.
b. Item 6: Engine Coolant Temperature Sensor.
c. Item 83: Power Steering Pressure Switch.
d. Item AC: Cylinder 1, 4 Heated Oxygen Sensor (front)
e. Item AD: Cylinder 1, 4 Heated Oxygen Sensor (rear)
f. Item AE: Cylinder 2, 3 Heated Oxygen Sensor (front)
g. Item AF: Cylinder 2, 3 Heated Oxygen Sensor (rear)
h. Item BB: Barometric Pressure Sensor
3. Turn the ignition switch to the "LOCK" (OFF) position.
Q: Are they operating properly?
YES : Go to Step 7.
NO : Repair or replace it. Then confirm that the malfunction symptom is eliminated.
STEP 7. Using scan tool MB991958, check actuator test.
1. Turn the ignition switch to the "ON" position.
2. Check the following item in the actuator test. Refer to MFI, Actuator Test Reference Table. Actuator Test Reference Table
a. Item 10: Evaporative Emission Purge Solenoid.
3. Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is the actuator operating properly?
YES : Go to Step 8.
NO : Repair or replace it. Then confirm that the malfunction symptom is eliminated.
STEP 8. Check the fuel pressure.
Refer to MFI, 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.
- 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 9. Check the ignition timing.
Refer to engine mechanical, On-vehicle Service -Ignition Timing Check.
Q: Is the ignition timing normal?
YES : Check the following items, and repair or replace the defective items.
a. Check the ignition coil and spark plugs.
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 valve.
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.