Checked everything possible, everything looked right... so I decided to pull off the TB and check the IACV... looked pretty clean, then I noticed the inside of it was rattling. Remembered I had an old Del Sol TB, so I pulled the IACV off of that one, and sure enough, no rattle. So, swapped the IACVs, at this point I'm 99% sure that had to be the problem. Waiting for some gasket maker to dry, so won't know til morning, though.