Never happen. Even my old stovebolt chevy's would ONLY ice up when the throttle is actually CLOSED... it has to do with the drop in temperature due to the increase in vacuum that occurs when the throttle is CLOSED.... and the engine is still turning at high RPM. "Coasting" in gear.... and actually in the case of the aforementioned Chevy's.... usually only when it's snowing.....

Not sure how it would happen with a T.B. but obviously, since even Ford decided to remove it, more than likely it's pretty much a non-event.

Particularly for me now.... being in SW FL and all that.