I second Herb's suggestions.
I would do the easy things first. Check the fuel pump and replace the fuel filter. Next I would send the injectors out for a proper cleaning and get them flow balanced while you are at it. There are injector cleaning and blueprinting specialists out there that will make the injectors perform better than new.
I don't think bad gas would cause any problems with the throttle body. You may have an issue with the throttle body but that would be a peculiar coincidence.
Straight lines are for fast cars...turns are for fast drivers
'04 M3 - track
'06 650i Cab - daily driver
'02 Highlander - kid hauler
'01 330Ci - winter beater