Problem with high idle....

[Da Bomb]

I have an '86 chevy K20 I use asa barn/plow truck. Recently it began to have a fast idle and foaled out the plugs. I repaced the plugs, got it runnig and found that the high idle would not kick down even after the truck came up to temp.. I remove the Rochester Q-jet nd had it rebuilt but this did nto solve my proble (looks shiney though!)
My question is...what controls the high idle? there is what looks like a temp. sender mounted in the t-stat housing that is wired back to a plug on the front left corner of the carb.
I'm at a loss and really am reluctant to spend $$ on a barn truck. Any help would be greatly appreciated.

Thanks,

Matt
in Freezin' NY