I had the same problem with mine after I did the coolant bypass. Turned out not to be a vacuum hose leak or an electical problem.
I blocked of that port on my TB and is fixed my problem completely.
BTW, I had a 96 S. And mine was jumping between 650 to 1400rpms. Hope this helps.
EDIT: sorry for the crappy pic but this best I can do right now.
__________________

96 Prelude R.I.P 6.26.04
www.ntpog.org
- Sneaky Doug (Genious with a Learning Disablity)
NTPOG President
71dsp's Monkey-Wrench-B!tch
To steal ideas from one person is plagiarism; to steal from many is research.