The idle control valve in your vehicle is mounted on the throttle body and controls the air flow into the engine from around the throttle body. The valve, as the name suggests, controls the idle. When this valve is dirty, your vehicle will have a hard time idling. Check to see if the valve is functioning properly by physically examining it. If it's dirty, you can clean it; if it's not dirty and your vehicle is idling rough, the control valve may have failed. You will be able to confirm this with a voltmeter.
Open the bonnet and remove the screws holding the idle control valve to the throttle body on the back of the engine.
Unplug the electrical plug running to the control valve. It may pull right off, but you may need to squeeze the release tab on the top of the your plug before it will come off the end of the valve.
Pull the idle control valve off the throttle body and turn it over to expose the valve openings.
Turn the dial on the voltmeter to "Ohms."
Touch one of the leads on the voltmeter to one of the terminals on the end of the valve. Then, touch the other lead of the voltmeter to the other terminal on the end of the valve. The reading should be "0.00," but a variance of ".05" is acceptable. If it falls outside of this range, your valve has failed and must be replaced.
Check the inside of the valve openings for dirt if the valve passed the ohm test (resistance test). The sensor will be dirty if the valve is otherwise functioning properly.
Spray the sensor liberally with electronic parts cleaner and allow the fluid to drain out of the valve openings until it runs clear.
Let the sensor dry completely and then reinstall it onto the throttle body. Installation is the reverse of removal.
Start your vehicle's engine and allow it to idle for several minutes so that the idle control valve can relearn the air flow required for the engine.
For specific information about checking your vehicle's idle control valve, consult the vehicle's manual (see Resources).