Chrysler Full-Size Vans 1989-1998 Repair Guide

Idle Speed Control Actuator

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OPERATION



See Figure 1

The Idle Speed Control (ISC) actuator is mounted to the throttle body and is controlled by the ECM. The ISC contains the idle contact switch and provides an input signal to the ECM. Various other sensors on the car give input to the ECM which help to control the ISC. The ECM supplies current and a ground path to the ISC actuator. This enables the ECM to increase or decrease the throttle stop angle by extending or retracting the ISC actuator. The throttle lever rests against an adjustment screw at the end of the actuator. The actuator extends or retracts to control engine speed and to set throttle stop angle during deceleration.

The ISC actuator is used on 1989-92 TBI vehicles. For 1992 MFI, as well as all 1993 and later vehicles, refer to the Idle Air Control (IAC) Motor procedure, earlier in this section.



Click image to see an enlarged view

Fig. Fig. 1: ISC actuator with its electrical connector removed-note the Idle Contact Switch circuit

TESTING



See Figures 2 and 3

  1. Remove the engine cover.
  2.  
  3. Remove the air cleaner assembly.
  4.  
  5. While watching the ISC actuator, have an assistant start the engine, shut it off and turn the ignition OFF . The ISC actuator should move outward to preset a fast idle after the next start, after the ignition is turned OFF . If it does not move outward, continue diagnostics. If the actuator moves outward, start engine and let idle to verify proper idle speed, if idle speed is out of specifications, set the idle speed using the procedure on reinstallation of the ISC later in this section.
  6.  
  7. Check the ISC actuator to see if it is frozen or sticking, if it is, replace it and retest. If it is OK, continue diagnostics.
  8.  
  9. Start the engine and backprobe the ISC connector to voltage is getting to ISC actuator. Voltage should be fluctuating between 2.0 and 6.0 volts. If voltage is OK, continue diagnostics. If voltage is not OK, repair circuit and retest.
  10.  
  11. Shut the engine off.
  12.  
  13. Disconnect the negative battery cable.
  14.  
  15. Disconnect the ECM wiring harness.
  16.  


WARNING
Testing the wiring harness with the ECM still connected can cause serious damage to the processor. ALWAYS disconnect the ECM before testing the wiring harness., unless instructed otherwise.

  1. Using an ohmmeter, measure the resistance on the ground circuit, using the supplied wiring diagrams, between the ISC connector and ECM harness connector. Resistance should be less than 5.0 ohms, if not repair ground circuit and retest. If resistance is OK, replace ISC motor.
  2.  



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Fig. Fig. 2: ISC actuator (motor) circuit schematic



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Fig. Fig. 3: Testing ISC circuit resistance with an ohmmeter

REMOVAL & INSTALLATION



See Figure 4

  1. Disconnect the negative battery cable.
  2.  
  3. Remove the engine cover.
  4.  
  5. Remove the air cleaner assembly.
  6.  
  7. Unplug the ISC connector.
  8.  
  9. Remove the ISC actuator retaining nuts.
  10.  
  11. Remove the ISC actuator from the bracket on the throttle body.
  12.  

To install:
  1. Install the ISC onto the bracket and tighten the retaining nuts.
  2.  
  3. Plug in ISC connector.
  4.  
  5. Connect the negative battery cable.
  6.  
  7. Perform the adjustment procedure.
  8.  



Click image to see an enlarged view

Fig. Fig. 4: ISC actuator mounting

ADJUSTMENT



See Figure 5

  1. If the engine cover is on, remove the engine cover.
  2.  
  3. Start the engine and allow it to run for two minutes.
  4.  
  5. Shut the engine off. Allow sixty seconds for the actuator shaft to fully extend.
  6.  
  7. Unplug the ISC connector and the ECT connector.
  8.  
  9. Hook up a tachometer to the engine.
  10.  
  11. Start the engine.
  12.  
  13. Adjust the extension screw on the ISC actuator shaft until the RPM is within the specifications.
  14.  
  15. On the 3.9L engine:
    1. If the vehicle has less than 1000 miles, set to 2400-2500 RPM.
    2.  
    3. If the vehicle has more than 1000 miles, set to 2500-2600 RPM>
    4.  

  16.  
  17. On 5.2L and 5.9L engines:
    1. If the vehicle has less than 1000 miles, set to 2650-2750 rpm.
    2.  
    3. If the vehicle has more than 1000 miles, set to 2750-2850 rpm.
    4.  

  18.  
  19. Shut off the engine.
  20.  
  21. Remove the tachometer from the engine.
  22.  
  23. Plug in the ECT and ISC connectors.
  24.  
  25. Install the air cleaner assembly.
  26.  
  27. Start engine and ensure that the idle is at specification.
  28.  
  29. Install the engine cover.
  30.  



Click image to see an enlarged view

Fig. Fig. 5: Adjusting the ISC actuator

 
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