1996 Buick Century

The car sputters when the car is in gear (i.e. stop light, drive thru, etc). Also, when passing on the highway, the car sputters when accelerating. This does not occur all the time but does occur on a dialy basis. I use 91 octane fuel. I tried using 87 about a month ago, then, switched back to 91.

Another question, where is the fuel filter on this car? Can I change the filter by myself or does it need to go to the dealership?

All help is appreciated!!!