hi all, i have a fiesta zetec 1.6 2003, not firing on cylinders 1 and 4, i replaced ht leads, spark plugs, coil pack, cam sensor, crankshaft sensor, and fuel filter............. car obviously idles rough, on some occassions when the revs are taken over 3k it drives fine and definetly appears to fire on all cylinders until revs drop below 3k then it goes back to only 2 and 3 and has very little power..... any suggestions?