REMOVAL & INSTALLATION
See Figures 1, 2, 3 and 4
- Disconnect the negative (-) battery cable and partially drain the radiator.
- Remove the air inlet duct and unplug the IAC and TPS electrical connectors.
- Label and disconnect the vacuum and coolant lines.
- Disconnect the accelerator, throttle valve (transmission control) and cruise control cables, as applicable.
- Remove the throttle body attaching bolts, then separate the throttle body from the plenum.
- Discard the gasket.
- Install the throttle body to the plenum using a new gasket. Tighten the bolts to specification.
- Engage the accelerator, throttle valve and cruise control cables, as necessary. Make sure that the linkages do not hold the throttle open.
- Connect the vacuum and coolant lines.
- Install the air inlet duct and plug the IAC and TPS electrical connectors into their sockets.
- Connect the negative (-) battery cable and refill the radiator.
- With the engine OFF, check to see that the accelerator pedal is free. Depress the pedal to the floor and release.
IAC Valve Position
The ECM will need to relearn the Idle Air Control (IAC) valve position anytime battery power has been interrupted to it. A scan tool must be used on 3.1L engines to update the ECM with the correct IAC valve position and provide a stable idle speed. The IAC valve position on others can be reset by starting and running the engine for 5 seconds, then turning the ignition OFF for 10 seconds. Start the engine again and check for proper operation.Minimum Idle Speed
The minimum idle speed should only be adjusted under two conditions:
If the throttle body has been replaced.
After every other possible cause for the incorrect idle speed has been explored.
There are many possible causes for incorrect idle speed, most of which require a high level of diagnostic skill as well as expensive testing equipment. Check the vehicle for vacuum leaks, incorrect valve or ignition timing, deposit accumulation in the throttle bore or valve, sticking throttle linkage or bent throttle valves. If the vehicle will still not idle properly after checking these areas, it should be diagnosed by a professional.
- Pierce the idle stop screw with an awl. Apply leverage to remove it.
- Make sure the IAC valve is connected. Short the A and B terminals of the ALDL connector together with a length of wire.
- Turn the ignition to the ON position, but do not start the engine. Wait at least 30 seconds before proceeding.
- With the ignition ON, disconnect the IAC valve connector.
- Separate the set-timing connector. This eliminates the possibility of changes in engine speed due to variations of engine timing.
- Start the engine and remove the wire shorting the A and B terminals together. It may be necessary to hold the throttle open slightly to prevent the engine from stalling.
- Allow the engine to reach normal operating temperature.
Adjust the idle speed to the following:
- 2.8L Engines - 450-550 rpm A/T or 550-650 rpm M/T
- 3.1L Engines - Refer to the underhood emissions sticker
- 3.8L Turbo Engines - 450-550 rpm
- 5.0L and 5.7L TPI engines - 400-450 rpm.
If these figures differ from those on the underhood emissions sticker, always follow the specifications on the emissions sticker.
- Turn the ignition OFF and connect the IAC valve harness. On models up to 1989, adjust the Throttle Position Sensor.
Throttle Position Sensor (TPS)
- Install three jumper wires between the TPS and the harness connector.
- Use a digital voltmeter connected to terminals A and B of the TPS.
- Turn the ignition switch ON, but do not start the engine.
Loosen the TPS attaching screws and adjust the sensor to the following:
- 2.8L Engines - 0.50-0.60 volts
- 3.8L Turbo Engines - 0.35-0.45 volts
- 5.0L and 5.7L TPI Engines - 0.47-0.61 volts
- Tighten the attaching screws, then check that the reading has not been disturbed.
- With the ignition OFF, remove the jumper wires. Reconnect the TPS harness.
- Start the engine and check for proper operation.