Idle Speed: Adjustments

Instructions:

NOTE: This procedure is to be performed only if the Curb Idle is NOT within the 900±75 RPM specification.





NOTE: Curb idle speed or Revolutions Per Minute (RPM) is controlled by the Electronic Engine Controller (EEC-IV) processor and the Idle Speed Control Air Bypass (ISC-BPA) valve assembly. If engine Curb Idle RPM is NOT within specification after performing this procedure, it will be necessary to perform the appropriate Electronic Fuel Injection (EFI) Turbo EEC-IV diagnostics.

1. Place the transmission in NEUTRAL, apply parking brake and TURN the A/C-Heat selector to the OFF position.
2. Bring the engine to normal operating temperature and turn OFF.
3. DISCONNECT the ISC-BPA power lead.
4. START engine and operate at 2,000 RPM for 120 seconds.
5. If electric fan comes ON during Idle Speed set procedure, wait for the fan to turn OFF before proceeding, or DISCONNECT it.
6. Let engine idle and check Base Idle RPM (750±50 RPM).
7. Adjust engine RPM to specification (Step 6) by adjusting throttle plate stop screw.
8. Shut engine OFF and RECONNECT:
a. Power lead to ISC-BPA.
b. Electric cooling fan.
9. Verify throttle plate is NOT stuck in the bore by exercising throttle plate.

NOTE: If excessive engine idle speeds are experienced when driving the vehicle on the idle system, TURN the ignition switch to OFF position and restart.