ive recenty done a RS2000 turbo conversion , we had the engine from a running donor car and transplanted it into my car , because the car was running on standard rs2k management it had a missfire at 3500 rpm so we changed the managment to fiesta turbo , the problem is the car will idle and rev fine whilst parked up but as soon as its under load (driving ) it'll cough and splutter and kangaroo along 10mph foot to the floor any idea's ?