Revs sat at 7k when engines off?

I have a 2005 mk6 ford firsta and my revs sit at 7k when engine is off, when I start it up it still sits around the 7k mark. When I'm driving the revs still go up as normal but just near the 7k not 0+k.
Iv disconnected the battery, it sorts the problem for a few hours then bounces back to 7k. Anyone have any idea what the problem might be? Thanks