I Have an idling problem with my 2005 Focus?

[CharlotteDod]

Hi we have had extremely cold weather here like -10 at times!!! I started the car early one morning and my car started revving on its on, only just slightly above 1 not alot but enough to make me jump as i didnt have my foot on the gas! I have a ford focus zetec 2005! Is it a big problem! I have a 3month warranty on the car and have only had it 2months so would like to get it sorted before it runs out thank u!