Thanks for the replies. I just finished building a variation of the smoke generator discussed on the link that Rowdie provided. So I'm going to give that a shot, in addition to closing off the hose to the ICV.

If it appears to be the ICV, I may try adjusting it per the instructions Dave Petryk provided here:
http://www.peachparts.com/shopforum/sl-forum/243090-idle-speed-air-control-slide-valve-confidence-check-2.html

And I'll post my findings as I get them.

Thanks again for the help.

DD