Inspection Procedure 8
INSPECTION PROCEDURE 8Unstable 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.
- Vacuum leak.
- Malfunction of the EGR solenoid system.
DIAGNOSIS
Required Special Tools:
MB991502: Scan Tool
STEP 1. Check if the battery terminal is disconnected Has the battery terminal been disconnected lately?
If no, go to Step 2.
If 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.
STEP 2. Using scan tool MB991502, read the diagnostic trouble code (DTC).
CAUTION: To prevent damage to the Scantool make, sure the ignition switch is "OFF" before connecting or disconnecting the scan tool.
If DTC is not output, go to Step 3.
If DTC is output, refer to Inspection Chart for Diagnostic Trouble Code.
STEP 3. Check the engine idling state.
If hunting badly, go to Step 4.
If hunting is not too bad, go to Step 6.
STEP 4. Check the following items.
(1) Carry out the following cleaning or adjustment.
a. Clean the throttle valve area.
b. Check and adjust the fixed SAS.
(2) After cleaning or adjusting, confirm that the malfunction symptom is eliminated.
If the malfunction symptom is not resolved, go to Step 5.
If the malfunction symptom is resolved, the check is completed.
STEP 5. Check for vacuum leaks.
(1) 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 6. Check the idle air control (IAC) motor operation sound.
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°C (68°F) or below is also okay.
(1) Check that the engine coolant temperature is 20°C (68°F) or below.
(2) Check the operation sound of the IAC motor can be heard after the ignition is switched "ON" (but without starting the engine).
- An operation sound should be heard.
If correct, go to Step 7.
If no sound is heard, refer to DTC P0505 - Idle Control System Malfunction.
STEP 7. Check the injector for operation sound.
(1) Using a stethoscope or long blade screwdriver, check the operation sound ("tick-tick-tick') of injectors during idling or during cranking.
- An operation sound should be heard. If a sound is heard, go to Step 8.
If no sound is heard, refer to DTC P0201, P0202, P0203, P0204 - Injector Circuit Malfunction.
STEP 8. Using scan tool MB991502, check data list and actuator test.
CAUTION: To prevent damage to the scan tool, turn the ignition switch "OFF" before connecting or disconnecting the scan tool.
(1) Check the following items in the data list.
Refer to Data List Reference Table.
a. Item 26: Closed Throttle Position Switch.
b. Item 13: Intake Air Temperature Sensor.
c. Item 25: Barometric Pressure Sensor.
d. Item 21: Engine Coolant Temperature Sensor.
e. Item 59: Heated Oxygen Sensor (rear).
f. Item 11: Heated Oxygen Sensor (front).
g. Item 27: Power Steering Pressure Switch.
h. item 28: A/C Switch
(2) Check the following items in the actuator test.
Refer to Actuator Test Reference Table.
a. Item 08: Evaporative Emission Purge Solenoid.
b. Item 10: EGR Solenoid.
If the checks above meet the specifications, go to Step 9. If the checks above do not meet the specifications, repair or replace. Then confirm that the malfunction symptom is eliminated.
STEP 9. Using scan tool MB991502, check data list.
CAUTION: To prevent damage to the scan tool, turn the ignition switch "OFF" before connecting or disconnecting the scan tool.
(1) Check the following items in the data list.
Refer to Data List Reference Table.
a. Item 45: Idle Air Control Motor Position.
If the check above meets the specification, go to Step 10. If the check above does not meet the specification, adjust the basic idle speed. Refer to Basic idle Speed Adjustment. After adjusting, confirm that the malfunction symptom is eliminated.
STEP 10. Using scan tool MB991502, check data list item 11: Heated Oxygen Sensor (front).
CAUTION: To prevent damage to the scan tool, turn the ignition switch "OFF" before connecting or disconnecting the scan tool.
- Voltage should fluctuate between 0 - 0.4 volts and 0.6 - 1.0 volts while idling after the engine has been warmed. If the voltage does not fluctuate, go to Step 11.
If the voltage fluctuates, go to Step 13.
STEP 11. Check the fuel pressure.
Refer to Fuel Pressure Test.
If correct, go to Step 12.
If incorrect, repair or replace. Then confirm that the malfunction symptom is eliminated.
STEP 12. Check the following items.
(1) 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.
STEP 13. Check the ignition timing.
Refer to Ignition Timing Check. If within specifications, go to Step 14.
If the standard value is deviated from, check and repair the crankshaft position sensor. Check that the timing belt cover is in the correct position. Then confirm that the malfunction symptom is eliminated.
STEP 14. Check the following items.
(1) 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.
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.