I already cleared the stored codes, and after a couple of driving cycles, I re-tried the scanner (even though the "!" "check engine light" was NOT on) and it gave me the same codes: "fuel trim - bank 1" & "fuel trim - bank 2." It also provided two dealer codes. I'll try the fuel additive/cleaner and premium petrol. Otherwise, if anybody else has ideas to add, feel free. Danke!