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Base Idle Setting Procedure

Applies To:

Range Rover Classic | '87-'88

Routine idle speed adjustment during maintenance services is not necessary nor desired. If your idling speed is off, it is often the result of another problem. The bypass air valve (stepper motor) located at the rear of the plenum chamber receives signals from the EFI's electronic control unit and automatically corrects hot idle speed within a range of 665-735 RPM. Use of air conditioning will raise the idle speed slightly above the normal range. This is acceptable.

Problems such as idle surge, excessively high or low idle or off idle hesitation can usually be traced to one or more of the following:

  • Incorrect throttle plate/throttle lever position
  • Incorrect potentiometer adjustment
  • Incorrect accelerator cable adjustment
  • Defective/disconnected road speed transducer
  • Ignition timing not within specification
  • Vacuum leaks
  • Incorrect fuel pressure
  • Loss of crankcase seal at oil filler cap or dipstick
  • Defective stepper motor or other EFI fault
  • Carbon build-up in throttle housing passageways
  • Basic engine condition - compression or leak down problems

Use the Workshop Manual, Lucas handheld tester and other shop diagnostic equipment to isolate and correct any of the above problems.

If the above checks, repairs or adjustments do not solve the problem, the base idle speed should be adjusted. IMPORTANT: All steps must be followed in sequence exactly as listed below. DO NOT attempt this procedure unless the basic throttle/timing/potentiometer adjustments have been made (see Workshop Manual - Section 19).

With the engine at operating temperature and an accurate tachometer connected:

  1. Center punch and drill (1/8" bit) the tamper proof plug located on the throttle housing.
  2. Remove the plug with a sheet metal screw and pliers.
  3. Discard the plug and clean up any metal chips.
  4. Switch the ignition on - DO NOT START THE VEHICLE.
  5. Disconnect the stepper motor plug.
  6. Switch ignition off.
  7. Listen for click from EFI main relay (under the right front seat).
  8. Reconnect the stepper motor plug.
  9. Switch the ignition on - DO NOT START THE VEHICLE.
  10. Disconnect the stepper motor plug.
  11. Start the vehicle in neutral without touching the accelerator.
  12. Adjust the base idle speed with a 3/16" Hex wrench to 550 to 650 RPM by turning the base idle screw. Turning counter clockwise will raise the speed and vice versa.
  13. Reconnect stepper motor plug.
  14. Switch ignition off.
  15. WAIT for main relay click.
  16. Switch ignition on, start the engine and rev briefly to 2000 RPM.
  17. Idle speed should stabilize at 665-735 RPM.
  18. Install new tamper proof plug.

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