P1351 Misfire cylinder 5 with fuel cut-off is kicking my ass! Latest is I have tried/noticed the following:

-moved coils and plugs; misfire stayed with cylinder 5
-i get a sharp rattle when accelerating above 2000 rpms
-when CEL comes on the rattle stops but car drags and runs rough
-check codes and 9 out of 10 times it is P1351, occasionally p1349 and p0300 as well
-i clear the codes and same cycle starts as above

now, the loud rattle dying off with CEL would seem to indicate that it is ignition related - once the computer shuts of that cylinder due to misfire, the car runs rough on 5 cylinders but rattle is gone. but what is causing the rattling? it seems to come from the rear of the engine, right where cylinders 5 & 4 would be.

thinking it was a vacuum leak from the intake breather hose, i replaced it and found some creamy caramel gook, pointing to perhaps oil separator issues - which make sense given i had it replaced a few months back but have been suspect since. however, would a bad separator cause the misfires and rattle? i don't believe it's vanos cause it's not coming from the front of the engine and it dies off when the CEL comes on.

any insight? please? really need to get this fixed as i depend on this car quite a bit...

thanks in advance!