Not going to start an oil thread but different oils carbonize/polymerize differently as well.
Originally Posted by German Steel
My 08 535xi @ 49,000 had same symptoms and had radical improvement after walnut shell blasting. Cost $575. You should see the squirills sniffing my tailpipe.
Apparently this carbonized oil buildup is minimized with high rpm driving ;-)
01 m5 - 127k miles 11/2013....08 535xit - 94k miles