Originally Posted by plumber212
I'm pretty sure we are 10% ethanol as well. What octane gasoline are you using. My dealer told me when I bought the car to run 89 octane. I questioned him since the owners manual says to run premium fuel. He explained that premium fuel in Germany is 89 octane.
I think your dealer is dyslexic. Premium fuel in Germany is actually 98 RON, which equals 93 AKI (the octane scale we use in NA). Regardless, octane has nothing to do with tailpipe soot. Soot is most likely a function of the DI fuel delivery and DI engines typically run very rich on cold starts. If your driving pattern is typically lots of shorter trips with fewer long ones there'll be more soot. Also, any oil consumption will contribute to fouled tips.
I've owned four vehicles with DI, and the only one that didn't have a lot of tailpipe soot was an F150 which was 90% highway driven.