High idle after engine swap

I'm really hoping someone can lend their expertise here. I've posted this question on here before, but still haven't been able to solve this problem of the engine idling high on my '98 Disco. It's now winter here in the great white north and it would be great if I could take the truck out without being worried that it won't stop if need be. The truck feels like a horse chomping at the bit whenever I pull up to a stop sign.

The engine was replaced with an engine from a '96 Disco and ever since it idles at 1500-2000 upon starting. Every now and again it starts up great and runs just like normal, but then it's back to the old high revving again after I restart. I've checked the TCM, and ICV. Someone suggested a vacuum leak-but the guy who installed the engine said he checked for leaks and didn't find any.

If anyone has some helpful suggestions I would really appreciate it. Thanks

http://www.roversnorth.com/forums/showthread.php?t=2200

Sounds like the same problem this guy had.