My Focus is coughing (rough) when accelerating

I have a 2001 Ford Focus ZTS 4 Cyl. 2.0(with double overhead cam and 78,000 mi) and it is coughing when I accelerate. It would usually smooth out when I reach my desired speed or if I accelerate slowly (very slowly). At appears to have an interruption in the gas flow. I changed the plugs and gas filter but it don’t help. I also took it to a mechanic but was unable to determine the problem. He suggested that I take it to the dealership but I wanted to get another opinion before I do that…dealerships are costly. I had the car for only 3-4 months; purchased it from a auction. It was originally a fleet car. Is there something I can do or have my mechanic check? We are both stumped.


I did not see air filter listed. Have you had it checked to see if any error codes were there? Some auto part stores will do that for free, like Autozone and Advanced Auto Parts.