Potential high idle solution

[Mark]

So this post isn't a question, but just sharing a solution I found to a high idle on an '84 automatic Tercel I was working on this weekend (not mine, but someone in the neighborhood). The engine idled at around 1500 rpm (just a guess, I didn't have a tach). I checked all the usual suspects like ruptured AAP diaphragm, vacuum leaks, stuck linkages, etc... , but all were good. Eventually I found the throttle positioner wasn't operating. The diaphragm wasn't ruptured, but the VTV (sort of a restriction/check valve) wasn't allowing vacuum through so the diaphragm wasn't holding the throttle closed and the spring was pushing the throttle slightly open as it's supposed to do during deceleration, but not at idle. There's a screw adjustment that I backed off to take this Throttle Positioner system out of commission since it wasn't working anyway. Now the throttle fully closes at idle and can be adjusted with the idle speed adjustment screw. I don't know if any of that makes sense, but here are some pictures from the manual:

Throttle positioner.jpg

Throttle positioner 2.jpg

Throttle positioner 3.jpg

Hopefully this might be of help to anyone driving themselves crazy trying to solve a high idle.

[dlb]

I think I've seen the VTV removed from the equation at least once but wasn't sure why a former owner would have done that. Now I think maybe they ran into the same thing as you.

[Mark]

I looked through one of your posts and it seemed like you had the same issue. A search for "throttle positioner" shows lots of other people had the same issue as well, so maybe not as obscure as I thought.