Replacing the Idle Air Control Valve (IACV)

What is the IACV?

The IACV is the Idle Air Control Valve and is a valve that is controlled by a stepper motor which in turn is controlled by the ECU. It is used to stabilise the tick over of your car by bypassing the throttle body with a controlled amount of air. This compensates for change of load etc.

It sits behind the throttle body and is bolted to the inlet plenum.



Why would I want to change the IACV?

The valve is a plunger which moves inside a tube.



It can totally seal or can move. The more it moves the more air it allows past the throttle body. Over the years there can be a build up carbon that forms on the plunger and inside the tube. This will prevent the smooth operation and correct sealing of the plunger so that the IACV cannot control the air as it should.

What are the symptoms?

If the IACV operation become impaired, the symptoms can be the engine hunting around a fixed point. Instead of idling around 800rpm, the engine will rise to 1200, drop to 700, rise to 1200 etc etc. Another symptom is a high tick over, such as idling at 1500rpm.

These can be caused by other problems, such as sticking throttle cable/throttle body etc etc, but these have been checked out in this case. It is also worth checking the IACV plug and socket for dirt/corrosion and positive fit as this could cause problems too.

To replace the IACV we need to remove the engine inspection cover.

You should then see the IACV between the top of the engine and the plenum chamber, just beside the oil filler cap..



To make life a bit easier I moved the rocker cover breather pipes to allow better access.



First, unclip the electrical connector by releasing the clip



And pulling the plug downwards until it releases



There are 4 Torx screws holding the IACV in place.



Remove all 4 Torx screws



And remove the IACV and associated rubber tube that attaches to the throttle body.



Remove the tube from the IACV and carefully remove the o-ring if you plan to re-use it.



Using a lint free cloth and some white spirit, clean the inside of the rubber tube as much as possible to remove any oily carbon deposits.



Refit the o-ring to the new IACV



And fit the rubber tube to the new IACV.



Now refit the IACV and tube, reusing the 4 Torx screws



And refit the breather tubes if you removed them earlier.

Now you should switch the ignition on and off several times to allow the IACV to find its reference points. This is the high pitched whistling noise that you hear when you turn your engine off.

You can now start the engine and hopefully all should work well.

It is worth mentioning that you should ensure that you buy the correct IACV as the old ones (Fs) don’t fit the TF and the TF has a 4 wire connection (the one in the pictures) and a five wire one. They are not interchangeable.

This is the one I bought.





Which is the 4 wire version.



It may be worth cleaning the IACV out with carburettor cleaner or similar, to try and remove any carbon etc. The older F version can be stripped down and cleaned, but the TF ones are sealed units.

Hopefully this will have sorted out any idling problems that you may have had.

How to reset the IACV video.

Added to the A-Z list of 'How tos' :thumbsup: