Computers and Control Systems: Adjustments
CONTROLLED IDLE SPEED CHECK1. 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, perform MINIMUM IDLE AIR RATE CHECK. If still not within specifications, refer to DIAGNOSIS BY SYMPTOM/DIAGNOSIS AND TESTING PROCEDURES/ROUGH, UNSTABLE OR INCORRECT IDLE.
MINIMUM IDLE AIR RATE CHECK
1. Check controlled idle speed and perform idle air control check first.
2. Set parking brake and block drive wheels.
3. START engine and bring it to normal operating temperatures 185-212 degrees Fahrenheit (85-100 degrees Celsius). Turn engine OFF.
4. Remove air cleaner, adapter and gaskets. Check that the throttle lever is not being bound by the throttle, throttle valve or cruise control cables.
5. With IAC valve connected, ground the diagnostic terminal (ALDL).
6. Turn ON ignition, DO NOT START engine. Wait at least 10 seconds (this will allow the IAC pintle to extend and seat in the throttle body.).
7. With ignition ON, engine stopped, test terminal still grounded, disconnect IAC valve electrical connector. (This disables the IAC valve in the seated position). Remove the ground from the diagnostic terminal.
8. Connect a SCAN tool to the ALDL connector and place in open mode. If a tool is not available connect a tachometer to the engine.
9. START engine. With transmission in NEUTRAL, allow engine rpm to stabilize.
10. Check rpm against specifications. Disregard IAC counts on SCAN tool with the IAC disconnected. If the engine has less than 500 miles or is checked at altitudes above 1500 feet, the idle rpm with a seated IAC valve should be lower than values in chart.
11. If the minimum idle air rate is within specifications, no further check is required.
12. If the minimum idle air rate is not within specifications, perform the following procedures:
13. If present, remove the stop screw plug by piercing it with an awl, then applying leverage. The screw is covered to discourage unauthorized adjustments.
14. With the engine at normal operating temperature 185-212 degrees Fahrenheit (85-100 degrees Celsius), adjust stop screw to obtain nominal rpm per specifications with seated IAC valve.
15. Turn ignition OFF and reconnect IAC valve electrical connector.
16. Disconnect the SCAN tool or tachometer.
17. Use silicon sealant or equivalent to cover stop screw hole.
18. Install air cleaner, adapter and gasket.
CONTROLLED IDLE SPEED
Transmission Gear Idle Speed IAC Counts [1] OPEN/CLOSED Loop [2]
Man. N 800 5-30 OL
Auto D 750 5-30 OL
[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).
MINIMUM IDLE AIR RATE
Transmission Gear Engine Speed [1] OPEN/CLOSED Loop [2]
Man. N 700 +/- 25 OL
Auto. D 625 +/- 25 OL
[1] If the engine has less than 500 miles or is checked at altitudes above 1500 feet, the idle RPM with a seated IAC valve should be lower than above values.
[2] Let engine idle until proper fuel control status (OPEN/CLOSED loop) is reached.