Why does my car rev while I am at a red light or in park sometimes?

What is your question?

Whenever I am parked (haven't really noticed it at a red light as much) but the car revs a little bit above 1000 and then comes back down and goes back to 1000 etc.. I don't know if this is bad and I have to get it looked at or if its okay. It only has just started to do this and it only happens once in a while. I don't hear any weird noises or anything else.

What makes this problem better or worse?

It has been pretty cold up here so I don't know if ts cause of the cold

How long has your 2005 Subaru Impreza had this problem?

I have just started to notice it.