So after cleaning the IAC and the RPM's running insanely high, my check engine light finally came on. I went on down to Auto Zone and had them run the diagnostic for me, and it showed the code for the IAC: P0505. When I got home, I ordered a new one and it arrived, so I went about installing it. Problem: despite being the same part number, the terminals are different. This one had rounder prongs and wouldn't fit.
Okay, back to the drawing board. I reinstalled the original and ordered another one, this one with blade style terminals. It arrives, and I take a comparison picture with the first replacement that I ordered:
Left side is rounder prong, right side is "blade style."
So I uninstall (unstall?) the original again, but this time I compare it to the new replacement:
Left side is "blade style," right side is original.
And that sonuvagun has bigger prongs, too. (You guys can mock me for getting parts off of ebay, now).
But by now, I'm determined, so I finagle it and work it and get it partially plugged in. I hook everything back up, and RPMs are high again. So I check for vacuum leaks, but I can't find any (yay?), and I keep the IAC plugged in but disconnected from the TB to make sure it is working, and it is, then I repeat with the original, and it's working, too. At this point, I'm just frustrated, so I spray the original and wipe off the little bit of gunk that has already been deposited since I cleaned it. I disconnect the battery, touch the cables together (I read somewhere that this discharges the capacitor and lets the computer reset (or reset easier, I forget), reconnect the original, and wait about an hour while I install the hood deflector, then reconnect the battery.
I'll be damned if it doesn't work like a charm now. Runs smooth, idles where it's supposed to, and I just had a great test drive - all with the original IAC. I don't know what I did. Maybe the 20 minutes I let the battery sit last time wasn't good enough, maybe touching the cables together helped, maybe I just tightened everything a little tighter. In any case, I have no idea, but I thought this would help in case anyone else runs into the same issues I did.