I run some injector cleaner every 5K miles or so.......actually, need to get some tomorrow, had a pretty rough idle when it started today, need to throw in some 93 octane as well. Normally I run Special instead of Premium. Chevron injector cleaner works well for me, mechanics have a nice can they hook up to the fuel line that burns all the crap out of the injectors, not cheap if I remember, about 60-70 bucks, have not done that on the BMW yet, but the car has 70K miles on it, might do that after I change my plugs soon.