Almost all throttle bodies are heated by the coolant. First mod I do is to bypass the coolant hoses.

This is what I believe.

The only time I have personally experienced this is back in the early 80's I had a Triumph TR7 with 2 Stromberg side drafts. No coolant hoses but did have the exhaust manifold heater tube and regulator on it for the air cleaner. Which I had disconnected.

So driving down the highway once cold foggy morning the car kept going slower and slower. I finally stopped and figured it out. Just sitting with the engine off heated the sliders up enough to break the frost.

I also put a temp probe just in front of the throttle body on my Gen Coupe once and saw temps below freezing at about 40F, this was when the throttle was closed at high rpm.

My understanding was that by preheating the throttle body, it would heat the air/fuel mixture enough to help it vaporize in cold weather. That would reduce smog during cold weather. This is one of the reasons that many carb and TBI V8 engines had a coolant passage inside the intake manifold underneath the carb or TBI unit. Also, I think heating the throttle body was also an alternative to using air cleaners which had snorkels routed over the exhaust manifolds.

This was less of a problem with inline engines which had the intake and exhaust manifold on the same side of the engine. Radiant heat rising from the exhaust manifold was often enough to aid in preheating the cold air/fuel mixture.

What about the IAC valve?

Most of the time, this emotionally driven behavior causes more harm than good.