Idle Speed/Throttle Actuator - Electronic: Testing and Inspection
***UPDATED BY TSB #89-16-003, June, 1989
System Schematic:
To test the Idle Speed Control (ISC) Servo (also called a Stepper Motor), located on the throttle body, proceed as follows.
OSCILLOSCOPE TEST
Oscilloscope Test:
1. Connect the probe of the scope to the pick-up points shown in the System Schematic.
2. Start the engine.
3. When the air conditioner is turned on, the idle speed will increase as the ISC control is activated. Check the pattern on the scope and verify the operation of the ISC motor. The scope pattern can only be observed when the ISC is operating. If scope pattern is not as depicted in image, continue with the rest of the test procedures before replacing the assembly.
INITIAL TEST
1. Check the ISC Servo motor to verify that sound can be heard from the motor after the ignition switch is turned on (without starting the motor).
2. If no sound can be heard, the ISC activation circuit must be checked. If the circuit is found to be normal, most likely the malfunction will be found in the ISC motor or the ECU.
CHECKING THE SERVO
1. Disconnect the ISC connector and connect the MD998463 special test harness if available.
(Special harness colored clip and harness connector equivalents. 1=red, 2=white, 3=blue, 4=black, 5=green, 6=yellow).
Component Test:
2. Measure the resistance between terminals 2 and 3 and 2 and 1 of the ISC connector.
3. Measure the resistance between terminals 5 and 4 and 5 and 6 of the ISC connector.
Standard Values:
Terminal 2 to terminals 3 and 1 28 to 33 ohm @ 68~F
Terminal 5 to terminals 4 and 6 28 to 33 ohm @ 68~F
Operation Verification:
4. Remove the throttle body and the ISC servo and hold the servo as shown in the image.
Test Connector Procedure:
5. Connect the 6 Volt power supply positive lead to both terminals 2 and 5. While connecting the negative (-) terminal of the power supply to each of the clips as described below, check the servo for a slight vibrating feeling as each connection is made.
CAUTION: Apply only a 6V DC or lower voltage. Application of higher voltage could cause damage to the stepper motor.
a. Connect the negative power supply lead to both terminals 3 and 6.
b. Connect the negative power supply lead to both terminals 1 and 6.
c. Connect the negative power supply lead to both terminals 1 and 4.
d. Connect the negative power supply lead to both terminals 3 and 4.
e. Connect the negative power supply lead to both terminals 3 and 6.
f. Repeat the test procedure in the reverse order from e to a.
6. If movement occurs during each step of the inspection, then the stepper motor is considered to be normal.
HARNESS TEST
1. Disconnect the ISC connector and turn on the ignition.
2. Using a voltmeter, measure the power supply voltage between ground and harness connector terminals 2, 5.
Voltage: System Voltage.
3. Turn off the ignition and disconnect the ECU connector. Using an Ohmmeter, check for continuity (short) to ground, between the ECU harness connector terminals 58, 59, 67 and 68 and the ISC connector terminals 1, 3, 4 and 6.
Continuity: Should Not Exist.
4. Using an Ohmmeter, check for continuity between the ECU harness connector terminals 58, 59, 67 and 68 and their coresponding ISC connector terminals 1, 3, 4 and 6.
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.