I agree, my first (and just about only) guess would be it's fuel pump or fuel filter related, and if you have a bazillion miles on the car the pump may well be nearing its end. The only other time when I noticed hesitation and momentary loss of power with my E21 was when I was low on fuel and took a turn fairly fast, apparently pushing whatever small amount of fuel was in the tank at the time away from the pump, causing the hiccup. Once straightened out everything was fine (and I headed directly to the gas station about 2 miles away). But this doesn't describe your circumstances, which could be more dire if it happens while on the highway. Other guesses-- fuel pump relay, fuel pressure regulator. Whatever, get it checked.