hi my rs fiesta misfires when you reach 70 mph and will not go on when you put the throttle down it makes car go worse you could say it makes her hoping mad any help by the way car be of road for 17 years and went though M O T first time thanks frankie:

 

Have you tried the standard procedure of changing plugs for a decent set of 071c, if not try a coil pack. Tell us how it fares mate

 

i will try this have a new coil and plugs the car only will do this in 4th sometimes but mainly in 5th from 70 mph on wards i was told to turn engine off and on some times it works but it only last while you drive on once you go back down and come back up the car start to miss again when you accelerate hard up from 1st 2nd 3rd car flies and no missing and it is doing in my head and wife will not drive car thanks again for your help and email frankie