Why does my Ford Ka misfire at midrange and then goes smooth again?

As it does not have a rev counter I might have over revved it once momentarily and ever since the orange engine light comes on and it misfires at +- midrange.Sometimes it runs smoothly right through the rev range.

Hi this is when the coil pack is showing signs of failure in the future so best to get it serviced at a ford dealer and tell them about this as they will need to fit a new coil pack.