I had the same issue on my 08 E92 and took it to the dealer. They found a SIB regarding an engine hose that has been failing and needed to be replaced. It took about a week to get the part from Germany. They replaced it and I haven't had the issue recur in the past 3000 miles. Before that, it was happening about 1 / week for 3 weeks and would clear itself after a few starts. My symptoms were exactly as you described.
Take it in and have your dealer look for the SIB. If they can't find it, let me know and I'll get the SIB info from my dealer and post it up for you.