Minimum Air Rate - Fuel Injection Only

NOTE: The minimum idle air rate is set at the factory with a stop screw and is not normally readjusted unless repairs or replacement of the throttle body assembly has occurred.

CONTROLLED IDLE SPEED CHECK

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, SEE DIAGNOSIS BY SYMPTOMS.



CONTROLLED IDLE SPEED
Transmission Gear Idle Speed IAC Counts [1] OPEN/CLOSED Loop [2]

Auto D [3] 5-50 CL

[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] Within 100 RPM from desired idle as noted on a SCAN tool.

NOTE: The minimum idle air rate is set at the factory with a stop screw, which is covered with a tamper plug. This setting allows enough air flow by the throttle valves to cause the IAC valve pintle to be positioned a calibrated number of steps (counts), from the seat, during "controlled" idle operation. If the IAC valve is disconnected and reconnected with the engine running, the idle speed may be wrong. In this case, the IAC valve can be reset by doing the following: while depressing the accelerator pedal about 1/4 down, start and run the engine for 5 to 10 seconds, the turn the engine OFF for ten seconds.
Engine idle speed is computer controlled through the IAC valve, by driving the IAC pintle in and out. Engine idle speed is a funtion of total air flow into the engine based on: IAC valve position, throttle valve opening (idle stop screw), calibrated leakage through the accessories, PCV flow. "Controlled" idle speed is programed into the ECM, which determines the correct IAC valve pintle position to maintain the desired idle speed.