There are times when I start the car that the car idles between 500 to 750 and I as wondering if that's normal or not?

Here's some info on the car:

I just purchased a S5 TII and was told by the mechanic that my #2 rotor is no good and that I'll have to do a rebuild in the future.

I'm wondering if the fact that my #2 rotor is not good contributing to this idle problem, any advise would be great.