Idle Speed

CONTROLLED IDLE SPEED

SPECIFICATIONS IN THIS ARTICLE UPDATED BY TSB # 90-206-6C.

NOTE: Before performing this check, there should be no codes displayed, idle air control system has been checked and the ignition timing is correct.

1. Set parking brake and block drive wheels.
2. Connect a SCAN tool to the assembly line data link (ALDL) connect with tool in Open Mode.
3. START engine and bring it to normal operating temperature.
4. Check for correct state of PARK/NEUTRAL switch on SCAN tool.
5. Check specifications chart for controlled idle speed and IAC valve pintle position (counts).
6. If within specifications, the idle speed is being correctly controlled by the ECM.
7. If not within specifications refer to COMPUTERS AND CONTROLS / SYSTEM DIAGNOSIS / TESTING AND INSPECTION / PROCEDURES / DIAGNOSIS BY SYMPTOM / ROUGH, UNSTABLE OR INCORRECT IDLE, STALLING.

UNDER 8500 GVW

Transmission Gear Idle Speed IAC Counts OPEN/CLOSED Loop

Man N 600 5-30 [1] OL [2]

Auto D 525 5-30 [1] CL [2]

[1] Add 2 counts for engines with less than 500 miles. Add 2 counts for every 1000 ft. above sea level.

[2] Let engine idle until proper fuel control status is reached (OPEN/CLOSED loop).

OVER 8500 GVW

Transmission Gear Idle Speed IAC Counts OPEN/CLOSED Loop

Man N 650 5-30 [1] OL [2]

Man [3] N 650 5-30 [1] CL [4] [2]

Auto D 550 5-30 [1] CL [2]

[1] Add 2 counts for engines with less than 500 miles. Add 2 counts for every 1000 ft. above sea level.

[2] Let engine idle until proper fuel control status is reached (OPEN/CLOSED loop).

[3] G van and Suburban with a single catalytic converter.

[4] Switches to OPEN LOOP after three minutes.