See Figure 1
The curb idle speed and mixture is controlled by the EEC-IV processor and idle speed control bypass valve.
This procedure should be performed only if the curb idle speed is not within 625-700 rpm for automatic equipped models, or 575-650 rpm for manually equipped models and all necessary repairs to the system have been made.
- Park the vehicle on a level surface and place block behind the wheels.
- Place the transmission in NEUTRAL and make sure the A/C-Heat selector is off.
- Start the engine and allow it to reach normal operating temperature, then turn the ignition off.
- Disconnect the idle speed control air bypass valve power lead.
- Start the engine and operate at 1,500 rpm for approximately 20 seconds.
- Allow the engine to idle and check that the idle speed is 550-600 rpm.
The engine may stall when the idle speed air bypass valve is disconnected. This is acceptable as long as the throttle plate is not stuck in the throttle body assembly bore.
- If the idle speed requires adjustment, disconnect the throttle cable and adjust the engine rpm by turning the throttle plate stop screw on the throttle body assembly.
- Reconnect the throttle cable, then recheck the idle speed and adjust, if needed.
- Once the idle speed is set, turn the engine OFF and reconnect the power lead to the idle speed control air bypass valve.
- Verify that the throttle plate is not stuck in the bore by moving the throttle plate linkage.
See Figures 2 and 3
The mixture is controlled by the EEC-IV processor and engine sensors. There is no manual adjustment. If the mixture is suspected of being either too high or low, check the electronic fuel controls. Consult Emission Controls for testing procedures.
- Place the transmission in PARK or NEUTRAL then start the engine and allow it to reach normal operating temperature.
- Turn the engine OFF , block the drive wheels and set the parking brake firmly. Turn all accessories OFF.
- Remove the Air Charge Temperature (ACT) sensor and adapter from the air cleaner tray by disengaging the retainer clip. Do not unfasten the connector. Remove the air cleaner, then disconnect and plug the vacuum line at the cold weather duct and valve motor.
- Start the engine, then turn OFF and verify that the Idle Speed Control (ISC) plunger moves out to its maximum extension within 10 seconds of key OFF .
- Disconnect the idle speed control. Disconnect and plug the EGR vacuum hose.
- Start the engine and manually open the throttle, then set the fast idle adjusting screw on the high step of the fast idle cam.
- Adjust the fast idle speed to specifications listed on the underhood sticker.
- Open the throttle manually to release the fast idle cam, allowing the throttle lever to rest on the ISC plunger.
- Loosen the ISC bracket lock screw. Adjust the ISC bracket screw to 2,000 rpm, then retighten the bracket lock screw.
- Reconnect the ISC connector. The engine rpm should automatically be adjusted to curb idle.
- Manually hold the throttle above 1,000 rpm
- Push the ISC plunger until it retracts fully
- After the plunger retracts, release the throttle and quickly unplug the connection.
- Adjust the anti-dieseling speed throttle stop screw to 750 rpm.
The anti-dieseling speed is NOT the curb idle speed.
- Reconnect the ISC and EGR vacuum hose.
- Stop the engine, then restart it to verify that curb idle speed is within specifications.
Curb idle speed is controlled by the EEC processor and the idle speed control air bypass valve assembly. The throttle plate stop screw is factory set and does not directly control idle speed. Adjustments to this setting should be performed only as part of a full EEC-IV diagnosis of irregular idle conditions or idle speed. Failure to accurately set the throttle plate stop position to the procedure below could result in erroneous idle speed control.
The mixture is controlled by the EEC processor and engine sensors. There is no manual adjustment. If the mixture is suspected of being either too high or low, check the electronic fuel controls. Consult Emission Controls for testing procedures.
- Place the transmission in NEUTRAL (MT) or PARK (AT), turn the A/C-heat selector to OFF, apply the parking brake firmly and block the drive wheels.
- Bring the engine up to normal operating temperature and check for vacuum leaks downstream of the throttle plates.
- Unplug the single wire, inline spout connector near the distributor and verify that ignition timing is 8-12° BTDC. If not, reset the ignition timing.
- Turn OFF the engine and disconnect the air bypass valve assembly connector.
- Remove the PCV entry line at the PCV valve.
- Install Orifice Tool T86P-9600-A or equivalent (0.200 in. orifice diameter) in the PCV entry line.
- Start the engine. The vehicle should be idling in DRIVE(AT) or in NEUTRAL (MT). Make sure the drive wheels are blocked and the parking brake is firmly set.
If the electric cooling fan comes on during idle set, unplug the fan motor power leads or wait until the fan switches OFF.
- Check the idle speed. It should be 820-870 rpm on models with an automatic transmission or 1,015-1,065 rpm on models with manual transmission. If the idle speed is not within this range, adjust by turning the throttle plate stop screw.
- Turn OFF the engine after the idle speed is set.
- Restart the engine and confirm the idle speed is within specifications after 3 to 5 minutes. If not, repeat setting procedure.
- If the idle speed is correct, turn OFF the engine, remove the orifice and reconnect the PCV entry line.
- Reconnect the distributor spout line, the ISC motor and the cooling fan power supply, if unfastened. Verify that the throttle plate is not stuck in the bore.
Idle speed and mixture are completely controlled by the EEC and EDIS system. No routine adjustments are required or possible. If idle speed or mixture is not within specification, consult an authorized dealer with the proper diagnostic equipment as soon as possible.