Idle Speed: Adjustments

Preliminary Note:

NOTE: The Curb Idle and Fast Idle Speeds are controlled by the Electronic Engine Controller (EEC-IV) processor and the Idle Speed Control (ISC) device.

Vehicle Prechecks:
1. Verify:
a. The cooling system is filled.
b. The throttle plate and throttle bore are clean.
c. Throttle is NOT sticking or binding.
d. The throttle lever is resting on the throttle stop screw.
e. There are NO vacuum leaks.
f. Heater and accessories OFF.
g. Engine at operating temperature.
2. Do:
a. Place transmission in PARK or NEUTRAL.
b. Apply the parking brakes (automatic brake release DISCONNECTED where applicable).
c. Block the wheels.
d. Check Curb Idle RPM, automatic transmission in DRIVE, manual transmission in NEUTRAL.

NOTE: If electric cooling fan comes ON, wait until it turns OFF.

3. If a rough idle problem exists, perform EEC-IV diagnostics and resolve any vehicle malfunctions that are indicated by service output code. (Ignore this step if you were sent here from a Pinpoint Test in Computers and Controls: System Diagnosis).
4. Check EEC controlled Curb Idle RPM, if it is NOT to specification, shut engine OFF. DISCONNECT the NEGATIVE (-) terminal of the battery for three minutes minimum then RECONNECT it. Let engine idle for five minutes with automatic transmission in DRIVE.
5. Check EEC controlled Curb Idle RPM, if it is NOT to specification shut engine OFF and follow the adjustment procedure for Base Idle RPM (see next step-Idle Speed Adjustment). Follow the procedure from top of the illustration in sequence to the bottom of the illustration.

Idle Speed Adjustment Procedures:

Idle Speed Adjustment
See illustration.

Figure 3:

Figure 3.