renault clio 172
is there anyone out there experiencing a flat spot on there 172, ive got a stainless steel exhuast and a k&n air filter ive recently changed the spark plugs because it was miss firing now ive got a flat spot and its driving me mad . in 1st and 2nd gear when i excelerate and reach 3000 rpm it feels like its holding back is there any one who can help