[Richard L]

I can see the OE throttle body is not a sealed unit and not intended to experience boost pressure. Small gaps within will allow some minor air leaks pass all the components. This means moisture will be introduced into the TB mechanism every time the system sprays. I cannot see a quick solution to your current problem other than smearing some thick grease on it and also spray the internals with WD40 which will repel surface water deposited during spray.

Possible solutions:
1. Does Mustang have a OE throttle body designed for SC applications?
2. What about spraying after the TB?
3. Relocate the jets at the exit of the IC.

Spray at the TB is by far the worse case scenario because the water mist does not have enough time to mix with the charge air properly and form a suspended droplet entity before plastering themselves onto the TB assembly.