The m103 can achieve almost 28-29 mpg when cruising on the freeway. In that smaller body, I can imagine you could* get 30mpg.

Start with fresh plugs and work your way back. I'd avoid tampering with lambda adjustments as you are running in closed loop.

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Eugene

10 E63 AMG
93 300te 4matic
07 BMW X3
14 Ford F-150 Fx2