1999 ford fiesta 1.25 16v

[Phim77]

Hi everyone hope someone can help yesterday my wife's car started misfiring now and again within 5 miles it's constantly misfiring now for the odd bit when ticking over no problem if you rev it slowly it revs till the limiter if you rev it fast ie foot to floor it missfires badly and driving is the same accelerate slowly no missfire try and take off normaly really bad ? Changed plugs, checked air filter removed checked and cleaned throttle body no fault codes stored?. Plug leads only couple of months old (ford) can someone help?.....