I have a 1994 Toyota Tercel that I like to let warm up in the morning before I leave for work. I live in the Northeast and right now it's pretty cold up here. Anyways, what I am finding is that when I go out to get in the car (after sitting idling for about 10-15 minutes) the heater is blowing cold air. NO warmth to it at all. The temperature gauge is up to normal. But as soon as I take it down the road, it starts putting out warm air. What can be causing this?