My 620s had the same symptoms as yours the TPS as Mark W Suggests is most likely way out.
Mine was at 60% throttle at idle..
My tps is on its 3rd adjustment.
Sadly IMHO.. Due to this and overfuelling my car with 3122 miles has 4 very badly scored Bores.
It has gradually got noisier on startup and sounds like a ring is broken when warm and cruising.
It is now parked up with 3122 miles, no track days.!
I may be just unlucky,
So it is not correct, get it sorted ASAP.