Fast idle, In search of air leaks Options

[Rand]

Been trying to nail the fast idle problem for a while. Have absolutely ruled out any vacuum leaks above the throttle body. Have replaced the injector seals. That leaves me with.... Leaking around the butterfly in the throttle body? Or somewhere else in the plenum or intake runner seals?

If I put my palm over the air intake, it does choke it down. That makes me wonder if air is getting around the butterfly (since the idle air adjustment screw is all the way closed). But I'm a noob on this detail... Please comment on this!!

I would think a crack in the plenum / air distribution box (whatever you wanna call the air box under the throttle body on a '75 2.0 Djet) would be rare. But I'm down to checking rare things on my list. I guess I don't mind taking all that apart because I haven't been there yet and wouldn't mind painting the plenum and air intake tubes anyway. Sooo.... Anyone have photos of disassembled plenum, intake runners, etc.? What will I need if I take this apart? (Seals/gaskets? Anything else?)