i have a problem with my escort GTi 1997.sometimes the car seems to misfire at 60-70mph when accelerating.also the car seems to lack power when accelerating .this does not happen all the time.sometimes the car feels like its running superb.i have changed the plugs,ht leads,coil pack and fiuel filter.after the fuel filter was changed the car ran perfect for a couple of days,then went back to misfiring and loss of power.please could anyone help.