So this was happening last winter but I couldn't figure out how to fix it. After my 05 tundra warms up the heater will still not blow hot air unless I start to rev the engine up a bit and its like something lets loose and it will blow hot air. However after a little bit it will start to blow cold air again and I have to do the process over again. Sometimes it works but others it just doesn't. Does anyone have an idea of what is going on here? Thank you!