Mine idles a little rough since new. I plan to take a look at the plugs to see how the gaps are. One or two or all could be off, you just never know unless you look. When the car is fully warmed up the idle is 500 rpms. With the air on its 550 or 600, hard to tell for sure on the tachometer. So I would guess its normal even if surprising. My other mercedes (m110 in line 6) is as smooth as silk.

Les