Try leads & coilpack first
Spark Plugs can help too...

I've known petrol Zetec engines to have a faulty EGR which has caused hesitation/misfiring.
If you try all these and STILL have juddery running or misfire and your getting no related fault codes - replace ECU. 100% fixes it. Petrol Ford ECU's (EEC-V) can fail and make them misfire.