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...