sorry to bring this back from the dead but i just did a tb cleaning and had a similar problem, but i have pin-pointed it to why it's doing it, i just don't know how to fix it. the idle is fine when i first start the car but as soon as it's revved it stays at around 2000 rpm untill i manually reach behind the tb and push the "valve"(?) back so that it idles. i think in the lexus repair manual they refer to it as the dashpot. anyway, it's not returning back to idle unless i push on it.
i'll try to get a picture of it and post it up here

 

that's my brother... and the owner in the background. I've ready a lot about oiling up the IAC and i'm not sure if people are talking about that, or the next picture i'm gonna show you.

 

that is where i pushed that valve in, which brought the car to an idle. whatever controls that isn't working, obviously. any help would be appreciated. i can take more pictures if needed. thanks

 

well i got it all cleaned up and put a few drops of oil in it, but it still doesn't seem to want to return to idle. I don't know what my next move is gonna be

 

The first pic is the IAC (idle air control motor), the 2nd is the
dash pot. I'm assuming it's a stick shift car w/ a dash pot on it.
Anyway the dash pot allows the throttle plate to close slowly,
instead of slamming shut in between shifts. Try running w/o it
& see if the RPM's still hang high. You really don't HAVE to have
it on the car, works w/o.

 

thanks for the help. after all day working on it... i've pretty much narrowed it down to the dashpot being bad. i tried to convince my brother to try it without it but this post will help me to persuade him.

 

Remove the cap from the rear of the dashpot (it is snapped on) and check the disk-like filter that's on the inside. They get really dirty and restrict the air from flowing out of the dashpot, making the dashpot close very slowly.

Good luck,

djl

 

did you confirm that the dash pot was bad? sorry to bring this back from the dead