Idle Speed: Adjustments

Throttle Body Assembly Exploded View:

NOTE:
a. The minimum idle speed should only be adjusted when installing a replacement throttle body.
b. The idle stop screw is used to regulate the minimum idle speed of the engine. On original equipment throttle bodies, it is adjusted at the factory, then covered with a plug to discourage unnecessary readjustment.

CAUTION: The minimum idle speed adjustment is critical to vehicle performance and component durability. Incorrect minimum idle speed adjustment (too high), will cause the IAC valve pintle to constantly bottom on it's seat and result in early valve failure. If minimum idle speed is adjusted too low, the vehicle may not start in cold weather or may stall during warm-up.

ADJUSTMENT:

1. Block the drive wheels, and set the parking brake.
2. Connect a SCAN tool to the ALDL connector.
3. Turn the ignition to the "ON" position.
4. Select "TPS" voltage display on the SCAN tool, and adjust the TPS to 0.54 +/- 0.08 volts.
5. Select "Field Service Mode" on the SCAN tool (refer to SCAN tool instructions). This will cause the IAC valve pintle to seat in the throttle body (closing the air passage). Wait at least 45 seconds, disconnect IAC valve connector, then exit "Field Service Mode."
6. Disconnect the distributor set-timing connector.
NOTE: The distributor set-timing connector must be disconnected to fix spark advance at base timing. This eliminates the possibility of changes in engine speed due to changes in timing.
7. Place the transmission in PARK (A/T) or NEUTRAL (M/T). Start the engine and idle until it reaches normal operating temperature, and CLOSED LOOP operation as read on the SCAN tool.
^ It may be necessary to hold the throttle open slightly to maintain idle.
8. Select ENGINE RPM on the SCAN tool, and read the engine speed:
^ Engine should be at normal operating temperature and in CLOSED LOOP.
^ Accessories (A/C, rear defog, etc.), and engine cooling fan should be "OFF."
^ Make sure the throttle and cruise control cables do not hold the throttle open.
^ Idle speed should be 425 +/- 25 rpm.
9. Adjust the minimum idle speed if necessary.
10. Turn ignition "OFF."
11. Connect the IAC valve electrical connector and distributor set timing connector.
12. Turn the ignition to the "ON" position, and recheck TPS voltage on the SCAN tool. Adjust if necessary, to obtain 0.54 +/- 0.08 volts.
^ Tighten TPS attaching screws to 2.0 Nm (18 lb. in.). Make sure adjustment did not change after tightening screws.
13. Reset IAC valve position:
a. Depress the accelerator pedal slightly.
b. START and run the engine for five seconds.
c. Turn the ignition "OFF" for ten seconds.
d. RESTART the engine and check for proper idle operation.
14. Disconnect the SCAN tool.
15. Remove the block from under the drive wheels.