I have a small problem with the car, it starts fine and runs but when i get to about 45/50 mph i get a small juddering, it feels like a spark plug is missing a beat, I have had all the plugs changed but the problem is still there, it only seems to happen when the car has warmed up a bit and not all the time, also when it is happening i sometimes get the engine management light flashing but not all the time, I have had it plugged into a computer but it shows up with no faults, Any help would be fantastic.

Phil Ward.