Hardhead: Before you dive in and start turning screws, removing and spraying parts etc, take a deep breath. Chuck and Tomguy gave you good advice now take a minute to go over it and the photo to orient yourself. First check that all your air supply hoses are tight and in good condition. The large ones going to the aux. air valve are the main air hoses. Check them and every, underlined, every vacuum hose under the hood. All should be pliable and tight on their fittings. On some eary D Jets the large main air hoses were clamped tight, but for some strange reason MB decided to save a few pfennigs and eliminate the clamps. Replace any suspiscious hoses and clamp them to ensure tight fit at all times.

You will have eliminated the obvious easy to fix sources of vacuum leaks. Check your vacuum with a gauge. Find a manifold source, at the back of the engine is where most easy connections can be made. You'll see the area back by the firewall where the lines come up from the maifold base and take off to the accessories. Somewhere in there you can find a place to tap into the vacuum for your gauge. If you have a very low vacuum reading, low normal could be 14-15"hg for an older engine, middle normal could be 16-18"hg. A low reading in the 12s or single digits and you have another big leak probably like the manifold seals Tomguy suggested. And if you do it will be affecting many other things on your engine. If you get something in the mid-teens then the manifold gasket is probably OK.

Next, try adjusting the large brass idle screw like Tomguy suggested. If it bottoms out w/o lowering the speed then air is coming in someplace. It is probable that your AAV is stuck open and no longer closing off as the engine temp rises. Try this site for a tutorial on AAVs: www.jag-lovers.org/xj-s/book/AAV.html
If it needs replaced, figure about $140 for the valve. It is fairly easy, but you may be able to clean it enough to get it working again.

If you have messed with the throttle body throttle plate screw instead of the idle air screw, then you'll need those instructions from Chuck or Tomguy to get it correct again.

230/8