5.3 idle is 600 I think this is low and sometimes the idle pulsates.

What type of damage would have been caused?

Yes in your climate it is necessary to have coolant warm the throttle body because of the cold temperatures in the winter. I live in southwest Florida. You really don't need throttle body warming here. Please do not play chemist with additives. More is not better.

Today I removed the throttle bodyand throughly cleaned, it was very dirty also changed the air filter. I will see how it reacts over the next couple of days. And whats with the coolent connection on the bottom of the T-body? does the coolent cycle around the T-body? Today - I don't know if my tach is wrong but my idle is now 500.