Borrowed from Ozliberty. Probably made by someone here ???
Copied & pasted.
Tools/Materials required:
Pliers
10mm spanner/socket&ratchet.
Contact cleaner
Carby cleaner/Subaru UEC.
Theory:
TThe IACV or Idle air control valve, operates to maintain a steady smooth idle.
After use, the valve can become blocked/restricted by gum and oil deposits.
Cleaning the valve should return normal idling characteristics.
Method:
Firstly Locate your IACV:
On turbo legacy's its located on the right hand side of the block (Looking from the front, as you would if standing looking at the engine.)
On Naturally aspirated Legacy's, its located on the opposite side of the throttle body. Its a bit of a pain to get to, but certainly possible.
The next step is to remove the hoses from the IACV. You'll need a pair of pliers to open the clamps, once the clamps are off the metal stub on the IACV, use the pliers to break the seal between the stub and the rubber hose, this will make it easier to remove the hose.
After this, you'll need to use either a 10mm spanner or socket, depending on what you find to be easiest. Remove the 4 bolts holding the IACV to the manifold. Once this is done you should be able to remove the IACV.
Once you remove the IACV, you should see this in the manifold:
Remove these if you wish to give them a quick clean, but take note of how they come out.
With the IACV removed, this is what you should see:
Clean the indicated places thoroughly, I normally keep flushing until the liquid coming out the other side is completely clean, then i turn it around and flush it the other way.
Under no circumstances should you remove the beige cap.
Replace the IACV, and replace the hoses securely.
Take note of the IACV bolts how ever. There are two different sizes.
The long one's go to the bottom, and the short ones to the top.
This is because the alloy mold has different lengths in the bolt holes. If you use the short bolts in the bottom hole's they will not reach. 
