Idle Air Control Motor (Stepper Motor)

Operation

The amount of air taken in during idling is regulated by the opening and closing of the servo valve located in the air passage that bypasses the throttle valve.

The servo valve is opened or closed by the activation of the stepper motor (incorporated within the idle air control motor) in the forward or reverse direction.

Battery power supply is supplied, by way of the multiport fuel injection relay, to the coil of the stepper motor. The engine control module switches ON the power transistors (located within the engine control module) in sequential order, and, when current flows to the stepper motor coil, the stepper motor is activated in the forward or reverse direction.


Troubleshooting Hints

Hint 1: If the number of stepper motor steps increases to 100-120 steps or decreases to 0 step, the cause may be presumed to be a malfunction of the stepper motor or damaged or disconnected wiring of the harness.

Hint 2: If the number of stepper motor steps deviates from the standard value even though the results of the checking of the harness of the idle air control motor and of the component itself indicate no abnormal condition, the cause may be presumed to be one of the following.

(1) Improper adjustment of the standard idling speed.
(2) Deposits adhered to the throttle valve.
(3) Leakage of air into the intake manifold from a gasket gap, etc.
(4) Incomplete close contact of the EGR valve seat.
(5) Incomplete combustion within the cylinder. (Malfunction of the spark plugs, the ignition coil, the injectors, the compression pressure, etc.)





Inspection


Using Oscilloscope

(1) Connect the probe to each oscilloscope pick-up point as shown in the circuit diagram.
(2) Start the engine.





(3) When the air conditioning switch is turned on, the idling speed increases to operate the idle air control. Check the instantaneous waveform.

Note: Keep in mind that the waveform can be observed only when idle air control is in operation.




Harness Inspection



Actuator Inspection

Checking the Operation Sound

(1) Check that the operation sound of the stepper motor can be heard after the ignition is switched ON (but without starting the motor).
(2) If the operation sound cannot be heard, check the stepper motor's activation circuit. If the circuit is normal, it is probable that there is a malfunction of the stepper motor or of the engine control module.


Checking the Coil Resistance

(1) Disconnect the idle air control motor connector and connect the special tool (Test harness).





(2) Measure the resistance between terminal 2 (white clip of the special tool) and either terminal 1 (red clip) or terminal 3 (blue clip) of the connector at the idle air control motor side.

Standard value: 28-33 Ohms at 2O°C (68°F)

(3) Measure the resistance between terminal 5 (green clip of the special tool) and either terminal 6 (yellow clip) or terminal 4 (black clip) of the connector at the idle air control motor side.

Standard value: 28-33 Ohms at 2O°C (68°F)



Operational Check

(1) Remove the throttle body.










(2) Remove the stepper motor.





(3) Connect the special tool (Test harness) to the idle air control motor Connector.
(4) Connect the positive (+) terminal of a power supply (approx. 6 V) to the white clip and the green clip.





(5) With the idle air control motor as shown in the illustration, connect the negative (-) terminal of the power supply to each clip as described in the following steps, and check whether or not a vibrating feeling (a feeling of very slight vibration of the stepper motor) is generated as a result of the activation of the stepper motor.

1. Connect the negative (-) terminal of the power supply to the red and black clip.
2. Connect the negative (-) terminal of the power supply to the blue and black clip.
3. Connect the negative (-) terminal of the power supply to the blue and yellow clip.
4. Connect the negative (-) terminal of the power supply to the red and yellow clip.
5. Connect the negative (-) terminal of the power supply to the red and black clip.
6. Repeat the tests in sequence from (5) to (1).

(6) If, as a result of these tests, vibration is detected, the stepper motor can be considered to be normal.