Land Rover Repair: 96 Discovery irratic idle, vacuum leaks, throttle linkage

Question
I have a 96 discovery that has a crazy idle.  Most of the time it jumps up to 2500 or more, but it's different every time I start it. No apparent vacuum leaks.  Have replaced the IAC and bought a used Mass Air. Runs great, but won't idle down.

Answer
If it's different every time I would first look for a mechanical problem in the throttle linkage.  I'd also look carefully at the throttle body.  If you don't find any explanation there the next step is to connect a t4 or autologic test system and look at all the engine data while it's idling.  If the car is mechanically at idle, and has no air leaks, the only way for it to speed up is by opening the idle air valve.  That can happen because the valve is bad (but you say you changed it) or because the computer commands it open.  If that's happening, the live data should show why.