If you plug the IAC hose shut and it's still idling fast, then either the throttle plate is not closing completely or you've got a gross vacuum leak somewhere, like a loose manifold or bad gasket, etc. Is the brake booster hose connected up good?

If you haven't done it already, maybe you should start at ground zero by cleaning the throttle body good, then make sure the plate is closing completely (adjust the stop), then adjust the TPS to the new plate stop position, then make sure the IAC is clean and its hoses are snug, etc, etc. Make sure the TPS is not so far out of adjustment that it is stopping the throttle plate from completely closing.

I'm not clear on what the "etc" is, but you say it melted ???