I was having the same type issues. I pulled the fast idle screw ( which was seated all the way) & replaced the o ring on it, seated it hard & retracted a few times, ran i a bit & found it lowered the idle.
FSM says to replace TB if idle will not lower.
I'd plug all vacuum hoses, including PCV & see what happens, then carb cleaner arount intake hose ( possible cracks) to diagnose it better.

Ed

Yankneck = Yankee ingenuity with Redneck stupidity.
"How can I break it better?"
89 Raider 3.0 w/ 31's for now