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 by-passes the throttle valve via IACV-AAC valve. The IACV-AAC valve changes the opening of the air by-pass 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-AAC valve movement causes the respective opening of the air by-pass 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 crankshaft position sensor (POS) 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
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-AAC 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.
DIAGNOSTIC TROUBLE CODE CONFIRMATION PROCEDURE
Perform "Procedure for malfunction A" first. If DTC cannot be confirmed, perform "Procedure for malfunction B".
Procedure for malfunction A
With Consult
1) Turn ignition switch "ON".
2) Select "DATA MONITOR" mode with CONSULT.
3) Start engine and let it idle.
4) Keep engine speed at 2,500 rpm for 3 seconds, then let it idle for 3 seconds.
Do not rev engine up to speeds more than 3,000 rpm.
5) Perform step 4 once more.
OR
With GST
1) Start engine and let it idle.
2) Keep engine speed at 2,500 rpm for 3 seconds, then let it idle for 3 seconds.
Do not rev engine up to speeds more than 3,000 rpm.
3) Perform step 2 once more.
4) Select "MODE 3" with GST
OR
Without Scan Tools
1) Start engine and let it idle.
2) Keep engine speed at 2,500 rpm for 3 seconds, then let it idle for 3 seconds.
Do not rev engine up to speeds more than 3,000 rpm.
3) Perform step 2 once more.
4) Turn ignition switch "OFF", wait at least 5 seconds and then turn "ON".
5) Perform "Diagnostic Test Mode II (Self-diagnostic results)" with ECM.
Procedure for malfunction B
With Consult
1) Open engine hood.
2) Start engine and warm it up sufficiently.
3) Turn ignition switch "OFF" and wait at least 5 seconds.
4) Turn ignition switch "ON" again and select "DATA MONITOR" mode with CONSULT
5) Start engine and run it for at least 1 minute at idle speed. (Headlamp switch, rear defogger switch: OFF)
OR
With GST
1) Open engine hood.
2) Start engine and warm it up sufficiently.
3) Turn ignition switch "OFF" and wait at least 5 seconds.
4) Start engine again and run it for at least 1 minute at idle speed. (Headlamp switch, rear defogger switch: OFF)
5) Select "MODE 3" with GST
OR
Without Scan Tools
1) Open engine hood.
2) Start engine and warm it up sufficiently.
3) Turn ignition switch "OFF" and wait at least 5 seconds.
4) Start engine again and run it for at least 1 minute at idle speed. (Headlamp switch, rear defogger switch: OFF)
5) Turn ignition switch "OFF", wait at least 5 seconds and then turn "ON".
6) Perform "Diagnostic Test Mode II (Self-diagnostic results)" with ECM.
WIRING DIAGRAM
DIAGNOSTIC PROCEDURE
COMPONENT INSPECTION
1. Disconnect IACV-AAC valve harness connector.
2. Check resistance between the following terminals.
terminal (2) and terminals (1), (3)
terminal (5) and terminals (4), (6)
Resistance: Approximately 3O Ohms [at 20°C (68°F)]
3. Reconnect IACV-AAC valve harness connector.
4. Remove idle air adjusting unit assembly (IACV-AAC valve is built-in) from engine.
(The IACV-AAC valve harness connector should remain connected.)
5. Turn ignition switch "ON" and "OFF", and ensure the IACV-AAC valve shaft smoothly moves forward and backward, according to the ignition switch position.
If NG, replace the IACV-AAC valve.