Idle Speed/Throttle Actuator - Electronic: Testing and Inspection

System Schematic:

The idle speed control (ISC) servo is a DC motor controlled by the ECU. It is used to regulate the amount of air that can bypass the throttle plate and affect the idle speed.

To test the idle speed control (ISC) motor, proceed as follows.

Component Test:

1. Disconnect the ISC motor connector.
2. Measure the resistance between the ISC connector terminals 1 and 4.

STANDARD VALUE
Terminals Measured Resistance
1 - 4 5 to 35 Ohms at 20°C (68°F)

Component Test:

3. Connect a "6 VOLT DC" power supply the the ISC connector terminals 1 and 4. this will extend or retract the servo depending upon the polarity of the power connection.

Caution: Do not apply more than 6 Volts DC to the ISC motor. Application of more than 6 Volts can cause locking of the motor gears, and damage to the motor.

4. Measure the resistance of the of the sensor as it is extended and retracted. There should be a smooth increase/decrease in the resistance, in the range of 0.5 k Ohms and the standard value, as the motor is extended and retracted. If the reading is not smooth the assembly should be replaced.


HARNESS TEST

1. Disconnect the ECU and ISC connectors. Using an Ohmmeter, check for continuity (short) to ground, between the ECU harness connector terminals 12 and 23 and the ISC harness connector terminals 1 and 4.

Continuity: Should Not Exist.

2. Using an Ohmmeter, check for continuity between the ECU harness connector terminals 12 and 23 and their corresponding ISC harness connector terminals 1 and 4.

Continuity: Should Exist.

If any of the previous tests produce unsatisfactory results, the harness will need to be repaired or replaced. Once repairs have been completed, road test the vehicle to confirm that the repair has corrected the problem.
If the same problem reoccurs, it is possible that there is an intermittent failure of the component or the ECU. Check for looseness at all harness junctions and test for an intermittent failure.