Peugeot 206cc 2004 idling too low?

I bought a peugeot 206cc 2004 last night. All seemed fine when i collected it, it didnt have much fuel in it so i went and filled it up on my way home. Drove it 30 miles down the motorway at a steady pace (didn't go above 70 mph) got home turned the engine off and when i started it again it is idling too low and sounds awful. has anyone got any ideas!!