I have a Fiesta.. 1.4i Duratec motor (2004). Had a few issues wrt misfiring. Replaced coil pack. New plugs. Car is fine except for a miss (lack of power) in the mornings. Cold Start. Also at the end of the day after the car has been standing. I removed the thermostat a while ago too and have not replaced it.
does your vehicle have an engine management light on