Symptoms of high idle, wandering idle or unstable idle can be often fixed by spraying some WD-40 brand lubricant into the right spots, and resetting the base idle. If this doesn't work, then these units may have to be removed from the car, disassembled and cleaned, then reinstalled. This short-cut is a lot easier and worth trying first. I do this job twice a year and I've never had to pull out my Idle Air Adjuster (IAA) or my air regulator. I highly recommend sticking with WD-40 for this work, which has just the right combination of cleaning and lubrication properties, IMHO.
The air regulator provides an air bypass when the engine is cold for a fast idle during warm up. The IAA is made up of the Auxiallary Air Control (AAC) valve, the FICD (Fast Idle Control Device) solenoid, and the idle adjust screw.
The IAA controls the idle speed of the engine based on the signal it receives from the car's central computer, the Electronic Control Unit (ECU). Idle speed is controlled through fine adjusment of the amount of air that bypassed the throttle valve via the AAC valve. The FICD solenoid controls a valve that increased idle speed when the air conditioner compressor comes on.
Disconnect and move this clutch booster hose to one side as shown by the blue arrow. The open end must be capped or blocked or the car will not run due to the large vacuum leak. I just set the end on a clean rag. The IAA is circled in yellow.
Disconnect the ground wires at the plenum shown by the yellow arrow. Then remove the short hose marked with the red X. The yellow X is the IAA. To the far side of the red X hose is the air regulator.
The first time I did this job the red X hose was brittle and hard as a rock, and tore during removal. I replaced mine with a 50 cent piece of 5/8" heater hose. You don't need the expensive, OEM preformed hose for this piece.
The red arrow shows where the hose red X went. Spray WD-40 into these two tubes with the car running. The top black tube goes to the air regulator. The bottom silver tube goes to the Idle Air Adjusting Unit. When possible, start with the engine cold and spray WD-40 into the black tube first.
The yellow circle shows where the ground wires in my fingers were attached. They are removed simply to make room to work.
If the car won't start with the tubes to the air regulator and IAA open, then you will need a buddy to start the engine while you stand there and keep these holes plugged with your fingers or some kind of temporary plugs to use betweeen sprays of WD-40. My car would run without plugging the holes, but barely. I could jump out of the driver's seat and get under the hood before the engine would die ;c)
As the car warms up, the vacuum will get weaker on the air regulator side and stronger on the IAA side.
After the cleaning procedure and the hoses are reconnected it's a good idea to reset the base idle. With the car warm, disconnect the yellow electrical connecter to the IAA show here.
If the car dies when the connector is unplugged, then the base idle is too low. Reconnect the harness to the IAA, restart the car and turn the idle screw shown below clockwise just enough so the car will run without the IAA connector plugged in, usually around 650 RPM's. The idea is to get the car to idle below 700 RPM without the IAA plugged in. Then, once the electrical connector is plugged back in, the IAA "takes over" and set the car's idle to spec according to the ECU, at around 750 RPM's. The idle screw is simply a back-up or fail safe setting in case the ECU cannot set the idle for some reason. The RPM's set by the idle screw are supposed to be below the ECU idle. Stock idle
Idle adjustment screw on the side of the IAA with long skinny Phillips screwdriver in place.