i think it is a common problem with 4.4 at cold temperatures. there are about 4 cars with similar symptoms over the last month on the russian bmw forum. it has something to do with a pipe which can be heated as a option but most people don't take this option. i didn't read all the details there as my X is not V8 but i will try to pass you their experiences on that. anyone here can translate technical terms from russian to english? i could just pass you the link.