My 2001 (produced Nov. 2000) 740iL with 86k miles has been making this chugging noise for a few weeks now. It happened a few days after changing the oil (using Mobil 1 Full Synthetic 5w30) and replacing the valve cover gaskets.
The evening it began, I had just replaced the fuel tank pressure valve, but it seems that's likely coincidental. I've heard that it could be the VANOS system. Edwin from Bimmerboard ran a can of Winn's Engine Cleaner (http://www.bimmerboard.com/forums/posts/642715
) and it seemed to make a difference, but i'm not sure his sounded as bad as mine does, and mine was a very sudden onset. It does have the usual VANOS clatter when starting it.
Could there be a problem with the oil i'm using, or something we might have done while replacing the valve cover gaskets? (they were a pain to get off and back on, but they're not seeping and we didn't hit anything.) I'm not quite sure what to do, would prefer to avoid Alderson BMW (The $tealer in Lubbock, TX.) I don't mind having a mechanic fix it if need be, though.
I do love this car, and i'd prefer not to bail on it, especially with only 86k miles on the clock.
Thanks in advance for your help, everyone. You'd be lifesavers if you'll help me figure this out.