Hi Nate I just left another phone mess/ w/ Collette w/ your # in it. she's been nutso busy w/ some real estate business, I know that can be hectic!
OK for your TB- what needs to happen is to determine the engine-on-at idle throttle position. I'd have to take another look, but is there a throttle stop adjust. screw on it? Put another way-w/ engine on, the dashpot retracts, right? So when it's retracted does the throttle plate fully close-or is there a tang on outside of throttle shaft contacting an idle stop screw? Heck simpler is to just remove the dashpot, and the throttle return spring on the shaft will put the throttle in it's idle position, long as I'm not missing anything else. I'll need better clearer pics of this wolly-bugger to say for sure, but I'm betting this TB is just about like any other except for the dashpot. Still scratching my melon as to why Toyota felt the need for the dashpot, musta been an issue w/ throttle sticking, why else? Don't usually see dashpots on TB's it's a sort of throwback to like 40-odd yrs ago. IF the throttle closes fully w/ dashpot retracted or removed, as in there is no idle stop screw- then that also tells me the IAC is always open some, that would be the only way air can enter if throttle is completely closed. IAC may even be open a little always, even if there is a throttle stop screw. Possible scenarios, just guessing here without benefit of holding it in my hands.
Also-remember to clean the IAC pintle and passageway well while it's off, I do this as part of initial TB cleaning, some carb. clean, a toothbrush and a dental pick for any hard deposits. On some engines, there have been cases of sudden uncontrolled engine RPM's caused by a dirty IAC sticking open, have heard stories of cars suddenly leaping ahead into an intersection w/o driver input, very bad news!
Would be good to see pics of this TB, if you clean it it will be easier to see what's up. But- it may also be useful to first treat it as we do w/ drive by wire GM TB's like Chevy Vortec 5.3's- before cleaning, look for the dark carbon deposit in the throttle bore right under the throttle blade-that will be another telltale of the "natural idle" position of throttle blade. I'm betting that when the dashpot is off of it it will be in that position, but I'd examine it carefully and be certain.
This, Nate, is all part of being a real Gadgetman, often there is "detective work" involved! I'm glad you have brought this one to our attention, gives the chance to think of this stuff!
thanks Nate!
Tracy G