So it almost sounds like what you are saying and that it may not be the heater core. I still have a strange smell coming through my vents that smells like something burning..not as strong today but still there. Anyway to test something like that? When I saw the smoke, I thought it was my wiper motor because it was getting stuck on the windshield due to light mist and a new super tight blade. It was coming up through a small vent on the outside of the car underneath the wiper arm. Maybe a water hose ruptured or something? The defrost won't get hot (just a little warm after a while) and same with the heater. Additional thoughts? and yeah, my car is still idling SWEEEEET!!!!