You got better mileage with 87 octaine?!?! I get an average of 50 miles more per tank with my 86 300e when I use 92 octain fuel than when I use the 87. That's how I justify the extra money. My car also runs a bit rougher on 87 than with 92. Interesting that you had the opposite results.
Kyle De Priest
2007 e320 Bluetec