my vote is for low compression on one hole. my rabbit fires up on 3 cylinders, and then picks the 4th as it warms up. it would idle on all 4 cold if i turned up the idle just a smidge. i know its not that bad because you dont have to bring the RPMs up much to make it pick off the dead hole. and like i say, its only when its dead cold. i dont run my car when its dead cold anyway. i dont like watching my oil pressure gauge peg the needle just off idle. cant be good for the pump or drive gear or tang. im sure thats where most of the wear in those oil pump drive tangs comes from.