Originally Posted by solishe
I have a 2009 335i Sedan with 45K miles. Started with same problem, so I decided to get a walnut shell blasting of my intake valves. That did not fix. Problem started getting worse and occurred during startup as well. Finally got misfire code on cylinder 5. My injector was replaced, problem solved. It can be a number of things (plug(s), coil(s), injector(s), or carbon buildup in intake, and potentially other things too. The initial focus should be on plugs, then coils, then injectors, followed by carbon buildup.
You can buy plugs for $100. Change them out and see if that solves the problem. If not, consider coils and injectors.