High idle at first...

I've got a 2003 Ford Focus LX 4 Dr. Sedan, with a 2.0L 4cyl. engine and a five speed manual transmission. When I first start it, the car idles at what I would guess to be about 2000-2500 rpm since I don't have a tachometer. If I wait a while or drive it, the idle slows down to a normal speed. I'm thinking this could be the the throttle position sensor or possibly the air valve sensor. Anyone else have this problem or know if I may be on the right track here?

In cooler ambient temps. they are supposed to have a high idle. how long does it run that fast? has it always done this or when did it start?