Idle RPM Check Procedure

VERIFY

NOTE: Idle RPM check should only be performed after Diagnostic Test Steps AIS7 through AIS9 have been completed.

- Transmission in PARK or NEUTRAL.

- Parking brakes applied (automatic brake release disconnectd where applicable.

- Driving wheels blocked.

- Generator belt tension.

- Heater and accessories off.

- Throttle lever resting on the throttle plate stop screw.

- EEC-IV diagnostics performed and vehicle malfunction indicated by Diagnostic Trouble Codes (DTCs).

NOTE:
- The curb idle and fast idle rpms are controlled by the Powertrain Control Module (PCM) and Idle Air Control (IAC) valve. The IAC valve is not adjustable. A large increase or decrease in closed plate airflow from the calibrated level will not allow this device to effectively control the rpm.

- Throttle bodies with sludge tolerant design are clearly identified with a yellow / black attention decal. This decal states that the throttle return screw must not be adjusted counter-clockwise (backed off), as this will not reduce the engine speed but may cause the throttle plate to stick in the bore in the closed (idle) position.

- Backing out the screw may be required if the throttle body had been previously serviced (a plug in the throttle plate orifice may by present) or if the throttle return screw has been tampered with (TP sensor self-test output out of range). The decal also advises that these throttle bodies must not be cleaned inside the bore, as cleaning will impair the sensitive coating. The sludge accumulation will not affect the throttle body idle air flow. (The cleaning procedure for the IAC valve may still apply.

Follow These Steps To Service The Throttle Body:
1. Remove the throttle body.
2. Hold it up to a light. No light should be visible between the plate and bore with the throttle plate closed. The hole in the plate should be visible and unobstructed.
3. Rotate the throttle lever and allow it to return. It should not stick or bind. It should return to the closed plate (idle) position freely when released. If the problem cannot be corrected (an obstruction cannot be removed, free sticking, etc.), the throttle body must be replaced.