The idle screw can be removed for cleaning, but somehow I doubt it will help much. It has a sort of rounded bullet nosed end. If it was dirty it would probably just have to be adjusted slightly differently.

The AAV is held on by 2 bolts - it sits on top of the block and the bulb penetrates into the coolant. It might be an idea to relieve the pressure on the rad first, but no coolant will leak out because everything else is below that level. It's a good idea to pick up a couple of gaskets first so you can remount it without leaks. I made my own out of some gasket paper.

I tried everything to get my AAV clean - soaked it in various solvents and detergents. Cycled it open and closed using boiling water and cold tap water. Sprayed Release-It and WD-40 into valve and let is sit overnight. I also squeezed the bulb a little so that valve would close more fully. It's a primitive device but I think mine now works properly.

You can get a good idea of whether AAV is leaking by if you squeeze the rubber elbow on the discharge side and cut off any flow (Engine speed reduces) You can also try disconnecting the elbow as in the picture and then put your thumb over the end of the rubber. That way you will get no air to idle valve and engine may stall if the idle screw is almost all the way in.

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5