In Reply to: "Fuel Quality Switch..." (more) posted by RobW on May 21, 2001 at 19:55:50:
Most folks will advise staying away from the little thing. Drastic engine changes may give you good reason to alter factory settings... I know of one E28 owner who swears by an alternate setting, but that's another story.
The factory setting is supposedly suited to the "quality" of a given country's fuel grade. I asked Conforti if the settings might could use tweaking (as fuel grades have certainly changed since the mid '80s) and he responded "leave the switch alone." (He said the same about the AFM in my '85 535i, but did I listen?) I left the switch alone, but tweaked the AFM with definite success. That's what I'd recommend, as well.
(That's my little story about that - that's if you care.)
Those anyone know for what porpouse is a screw driver hole in the computer, looks like for some kind of adjustment.