All I will say is that I thought I had ruled out vacuum leaks on several of my cars and then awhile back I learned the "cheap cigar" trick and found leaks in places I never would have seen, and I'm not even sure why I thought I had X-ray vision...
Basically, just connect some tubing to a spare port on the intake and blow smoke in it. I don't smoke, so a $1 cigar from the gas station filled the need.
Now, if you've done that already then you definitely have ruled out vacuum leaks.
Aside from that, does it still rev if the idle stabilizer valve is unplugged? While the ISV doesn't actually control the idle like most people think, it could be sticking or is getting a signal to boost the idle when it doesn't need to (idle switch under the throttle body I believe).
I think that's about it. Not much to them as far as that goes.