I just noticed this on mine today. I took it out for a run as I wasn't sure if there was water in the exhaust system. It cleared up and was fine after warming....
At the moment I'm led to believe either AOS or head gasket......kind of hoping the former.
On a plus side, I've replaced the MAF sensor today, and the car idles much more stable now. Not as stable as I'd like to be honest, but much better
