2002 Ford Taurus rough, hesitating

I am having a problem with my 2002 Ford Taurus. All of a sudden it started riding very rough and hesitating when accelerating. If I am in park you don't notice it as much. If the car is in drive and you are trying to accelerating it doesn't want to go faster. Have to let up on the gas then give it a little gas. Is much worse if you turn on the airconditioner. Terrible when at a stop light or in stop and go traffic. Check engine light always on and the computer says it is a misfire in cylinder one. I have replaced all spark plugs and leads. Changed out the pvc gasket and fixed a collapsed vacuum line. Nothing works.