It depends how rough the idle is. In my X3 2.5i petrol, I feel it is sensitive to excessive ambient humidity for some reason. On very wet days, it will crank a bit longer, and there is a very very mild shaking for 10-15 seconds before I drive off. I think my condition is normal since it has occured for quite a while. However, if your condition persists for longer than a few seconds, you might need to get it looked at.

Any unusual noises?