P0505

SYSTEM DESCRIPTION
This system automatically controls engine idle speed to a specified level. Idle speed is controlled through fine adjustment of the amount of air which bypasses the throttle valve via IACV-AAC valve. The IACV-AAC valve changes the opening of the air bypass passage to control the amount of auxiliary air. This valve is actuated by a step motor built into the valve, which moves the valve in the axial direction in steps corresponding to the ECM output signals. One step of IACV-MC valve movement causes the respective opening of the air bypass passage. (i.e., when the step advances, the opening is enlarged.) The opening of the valve is varied to allow for optimum control of the engine idling speed. The camshaft position sensor detects the actual engine speed and sends a signal to the ECM. The ECM then controls the step position of the IACV-AAC valve so that engine speed coincides with the target value memorized in ECM. The target engine speed is the lowest speed at which the engine can operate steadily. The optimum value stored in the ECM is determined by taking into consideration various engine conditions, such as during warm up, deceleration, and engine load (air conditioner, power steering and cooling fan operation).

COMPONENT DESCRIPTION

IACV-AAC Valve
The IACV-AAC valve is operated by a step motor for centralized control of auxiliary air supply. This motor has four winding phases and is actuated by the output signals of ECM which turns ON and OFF two windings each in sequence. Each time the IACV-MC valve opens or closes to change the auxiliary air quantity, the ECM sends a pulse signal to the step motor. When no change in the auxiliary air quantity is needed, the ECM does not issue the pulse signal. A certain voltage signal is issued so that the valve remains at that particular opening.

Consult-II Reference Value In Data Monitor Mode:

On Board Diagnosis Logic:

DTC Confirmation Procedure

NOTE:
- If "DTC Confirmation Procedure" has been previously conducted, always turn ignition switch "OFF" and wait at least 10 seconds before conducting the next test.
- Perform "Procedure for Malfunction A" first. If 1st trip DTC cannot be confirmed, perform "Procedure for Malfunction B".
- If the target idle speed is out of the specified value, perform "Idle Air Volume Leaning", before conducting "DTC Confirmation Procedure". For the target idle speed, refer to "SERVICE DATA AND SPECIFICATIONS (SDS)".

PROCEDURE FOR MALFUNCTION A

TESTING CONDITION:
Before performing the following procedure, confirm that battery voltage is more than 10.5 V with ignition switch "ON".

With CONSULT-II
1. Turn ignition switch "ON".
2. Select "DATA MONITOR" mode with CONSULT-II.

3. Start engine and let it idle.
4. Keep engine speed at 2,500 rpm for three seconds, then let it idle for three seconds.
5. Perform step 4 once more.
6. If 1st trip DTC is detected, go to "Diagnostic Procedure" below.

With GST
Follow the procedure "With CONSULT-II" above.

PROCEDURE FOR MALFUNCTION B

TESTING CONDITION:
- Before performing the following procedure, make sure battery voltage is more than 11 V at idle.
- For best results, perform the test at a temperature above -10 °C (14 °F).
- Electrical load not applied.

With CONSULT-II
1. Open engine hood.
2. Start engine and warm it up to normal operating temperature.
3. Turn ignition switch "OFF" and wait at least 10 seconds.

4. Turn ignition switch "ON" again and select "DATA MONITOR" mode with CONSULT-II.
5. Start engine and run it for at least 1 minute at idle speed.
6. If 1St trip DTC is detected, go to "Diagnostic Procedure" below.

With GST
Follow the procedure "With CONSULT-II" above.