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 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 Diagnostic Trouble Code Chart Multiport Fuel Injection (MFI).
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 On-vehicle Service - Clean the throttle valve area 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. 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 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 Data List Reference Table Data 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 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. 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.
a. Item AC: Cylinder 1, 4 Heated Oxygen Sensor (front)
b. Item AE: Cylinder 2, 3 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 10.
NO Go to Step 9.
STEP 9. 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.
- Vacuum leak.
- Broken intake manifold gasket.
- Broken air intake hose.
- Broken vacuum hose.
- Positive crankcase ventilation valve does not operate.
b. Injector clogged.
NO Repair or replace it. Then confirm that the malfunction symptom is eliminated.
STEP 10. Check the ignition timing.
Testing and Inspection.
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.