On the 1.3 Endura Engine it's supposed to be 1.1mm gap(1.3mm on other Fiesta engines).
I have been trying everything and have the same trouble. I have changed the plugs, filters (air & oil), leads, cleaned the silver thing on the front of the efi and other things. The car runs ok for a while and then back to square one. It misfires whilst driving and cuts out at lights/junctions/roundabouts. Took it to Ford and they found nothing. I have had a tit full.
