A lambda sensor is just that, ie it does not know what engine it is attached to.
In the first instance, the cams on a zetec are not keyed so can be set in any position, even incorrectly.
I would start at the stupid stuff first, put to the std cam settings, with bar in the rear of cams, and peg etc.
Make sure there are no air leaks, clean the maf, reset the ecu by pulling the 2 amp fuse marked KAM, then see where you go from there.
I take it it has different cams to std when you say cammed ?, if you know the spec dial the cams in as per the makers timing figures, check the fuel pressure is correct, make sure the fuel filter is new.
tabetha