By "under the throttle plate", I mean in the intake tract past the throttle plate, like an unported* vacuum port, carb base gasket, intake manifold gasket, brake booster hose.

*Unported vacuum port is one in which vac is applied when the carb is at idle position. Ported vac is a vac port that only has manifold vac when the throttle is moved past the idle stop. If you look at the vac diagram in the FSM, you will see some vac ports are above the throttle plate when it's at idle stop. Those are the ported vac. For example, you usually don't want egr at idle, so you acutate the egr valve with ported vac so it only opens when the throttle is opened past idle.

I hate carbs...

No, a stuck float won't act like that, usually. It sure won't cause a high idle by itself.

You have a vac leak, I betcha...

Thanks for the pointers, FastEddie. I'll poke around on my next off day and see what I can find.

I wouldn't go that far exactly, if you adjust it a tiny bit at a time and see the results its a good way to resolve most idle issues. On occasions adjusting the idle on the Mikuni fixed the problem. I would say be careful and adjust it only a little at a time, because not many people have the manuals.

At least you got a little bit of improvement from adjusting the idle. Sucks to hear your probably have a vaccum leak. Just remember if you go taking off all the hoses label them accordingly so when it comes time to re-connect them you don't have too much of a headache. Best of luck with it.