Chrysler Full-Size Trucks 1967-1988 Repair Guide

Minimum Idle Speed Adjustment

Print

Normal idle speed is controlled by the SMEC. This adjustment is the minimum idle speed with the Automatic Idle Speed (AIS) closed.

  1. Before adjusting the idle on an electronic fuel injected vehicle the following items must be checked.
    1. AIS motor has been checked for operation.
    2.  
    3. Engine has been checked for vacuum or EGR leaks.
    4.  
    5. Engine timing has been checked and set to specifications.
    6.  
    7. Coolant temperature sensor has been checked for operation.
    8.  

  2.  
  3. Connect a tachometer and timing light to engine.
  4.  
  5. Close the AIS by using ATM tester C-4805 or equivalent. Enter ATM test code #03.
  6.  
  7. Connect a jumper to radiator fan so that it will run continuously.
  8.  
  9. Start and run the engine for 3 minutes to allow the idle speed to stabilize.
  10.  
  11. Check the engine rpm and compare the result with the specifications listed on the underhood emission control sticker.
  12.  
  13. If idle rpm is not within specifications, use tool C-4804 or equivalent to turn the idle speed adjusting screw to obtain 790-810 rpms. If the underhood emission sticker specifications are different, use those values for adjustment.
  14.  

If idle will not adjust downward, check for binding linkage/throttle shaft or improper speed control servo cable adjustment.

  1. Turn off the engine, then disconnect the tachometer and timing light. Remove the jumper wire from the fan motor. Remove the ATM tester.
  2.  

 
label.common.footer.alt.autozoneLogo