Since getting my 325i new in '95 there's been a quirk with the car I haven't been able to chase down. Upon easy acceleration I encounter, with varying severities, a hesitation or stumbling, occasionally even a bucking, in the 1800-2000 rpm range. On either side of that everything runs smoothly, but if I set the cruise control in that range there's almost a guarantee of rougher going, and when accelerating through that rpm range I get a distinct feeling of back pressure coming through the gas pedal, almost as if the car is resisting me. Weird, for sure.
Early on, those many years ago when the car was still under warranty, I took it to the dealer, but didn't get much other than "these cars are meant to be driven hard," that and a couple bottles of Techron. Changes of spark plugs, air filter, fuel filter have some, but not an entirely satisfactory, result. The injectors have not been touched. Then again, there have been times when the phenomenon has completely, and mysteriously, disappeared and the engine pulls cleanly and smoothly through the 1800-2000 range, but it's there more often than not.
My driving style is very much on the easy side, mostly highway with the cruise control set between 70 and 75 (well, okay, there have been a few stretches of 100+, but only when road and traffic conditions permit), always use brand name 93 octane (occasional use of 91), oil and filter changes at 5000 mile intervals, service intervals are followed. I haven't come across any similar mentions of this occurence, and since I've had this since day one, and it seems to defy the more plausible explanations, as well as the passage of time (and miles), maybe it's just a sometimes annoying idiosyncracy, akin to a birthmark. But any thoughts, suggestions, similar experiences would be appreciated.