Idle Speed: Adjustments

NOTE: Curb and fast idle speeds are controlled by the Powertrain Control Module (PCM) and Idle Air Control (IAC) valve assembly. The IAC valve and idle speed is not adjustable. A large increase or decrease in closed plate airflow from the calibrated level will not allow effective idle speed control.

Throttle Body Assembly Decal Location:

Throttle bodies with sludge tolerant design are identified with a yellow/black decal. The throttle body must NOT be cleaned inside the bore, as this cleaning will impair the sensitive coating. Sludge accumulation will not affect the idle air flow. The cleaning procedure for the IAC valve still applies.

RPM LIMIT CHECK PROCEDURE - Self-Test constant tone
STAR tester or equivalent scanner required

1. Activate engine running Self-Test.

2. After diagnostic trouble code 11 or 111 has been displayed, unlatch and within 4 seconds latch the Self-Test Input (STI) button.

3. A single pulse code indicates the entry mode, then observe the Self-Test Output (STO) of the STAR tester. A constant tone, solid light or "STO LO" readout indicates base idle rpm is within range.

4. To exit test, unlatch STI button, then wait 4 seconds for reinitialization (after 10 minutes it will exit by itself).

5. If the idle rpm is not within limits, eliminate the following possible causes:

- Battery and charging system integrity

- Contamination within the IAC component

- Lack of fuel system control (excessively rich or lean)

- Throttle sticking or binding

- Engine not reaching operating temperature

- Incorrect ignition timing

- Incorrect or clogged PCV system

- Vacuum leaks (intake manifold, vacuum hoses, vacuum reservoirs, power brake booster, etc.)

- Exhaust system, EGR.