A leaking valve cover just boils down to a vacuum leak. Any air that is unmetered after the MAF will cause the motor to run funny. Now with the valve cover, if there is a very very slight leak, you will not notice a difference... but if the leak is severe enough, sure it will cause a misfire issue. While IL's are the official "fix" for BMW NA, but a lot of people have reported to do the fix, only to have the problem come back the next year.

To do a simple search, remove the diaphragm and check for the cheese... I've also realized that spring is also very critical... When I replaced the ones in in mine... just to see, I measured the springs... Now I know this isn't the official correct way because there is alot of variables, but just taking measurement with a set of dial calipers, the old ones compared to the new ones, there was a difference of .003... Old ones, I had a rough idle. New ones, idle fine. New diaphragm old spring, rough idle. Old diaphragm new spring, idle is fine. So the tension of the spring is important. If you can't remember when you replaced yours, it's a cheap enough fix to do.

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2011 E70 50i M Sport