During acceleration the engine stumbles. This happened randomly on the highway and noticed when first stopped and then continued on. the only thing I noticed is that the fuel attendant failed to screw on my gas cap, I put a couple of hundred miles on the car with the cap off. Everything is original on this car other than routine maint. parts. I believe the fuel filter is original as well. Vacum operates correctly, according to my Haynes man. Thanx for the consideration!