High or Low Idle Issues

Idle Problems


  • Idle speed is erratic, speed varies up and down Idle speed is too high or too low
  • Idle speed cannot be adjusted to specification

Diagnosis Procedure:

  • Adjust idle speed
    • Idle speed should be checked and adjusted to within specifications. If the idle speed is too high, the centrifugal advance in the pump may begin to work. This could result in symptoms of high or erratic idle.
  • Check adjustment of accelerator cable and lubricate injection pump lever
    • Unless the accelerator cable is adjusted properly, the injection pump lever may not touch the idle stop. It is also important to lubricate the injection pump lever to assure that it moves freely on its pivot.


  1. Adjust idle and maximum speed
  2. Lubricate accelerator cable and lever
    • Lubricate accelerator lever return spring with spray lubricant (WD 40 or equivalent).
    • Check to ensure that the accelerator lever rests against the idle adjustment stop.
    • Check to ensure that the accelerator lever moves freely and does not stick.
    • Depress the accelerator pedal fully and check to ensure that the accelerator lever contacts the maximum speed adjustment stop.
      If the accelerator cable is out of adjustment


Cars with manual transmission

  • If the throttle linkage is out of adjustment,
  • Loosen cable locknuts
  • Depress accelerator pedal fully
  • Adjust cable so that throttle lever contacts maximum speed screw and is not strained.

Cars with automatic transmission

  • If throttle linkage is out of adjustment,
    See this link.



Quality check

  • With fully warmed engine, raise engine speed to 3000 RPM for about 5 seconds
  • Release the injection pump lever and let the engine return to idle.
  • Measure idle speed with tach and check that:
    1. The idle speed is correct
    2. The idle speed does not vary more than 50 RPM
    3. The idle is not rough

If test passed, return car to customer

If test failed, perform diagnosis procedure II