Last month when I had my valve cover gasket replaced my mechanic noticed that the spark plugs had a yellow burn on them instead of brown. He told me that my car was running lean.. I didn't have a clue as to what he was talking about so I started sniffing around. On M3forum I heard a guy talking about an Oxygen sensor so I decided what the hell I'll get one... I also remember Jack at Benzin testing my car out and telling me that mine was bad.. So I ordered one... It just came to the office this morning.. I am counting down the hours till 5 so I can put it on.... I hope it makes a difference, it would be cool if my M started running rich and I am able to beat C5 vettes....
:alright

I'll post the results tomorrow.....

i can sell you some back ups??
i have a brand new one and an old one just lying around and need the cash

u should actually feel more performance when running lean. thats how all the people i know blew their motors. they felt their cars running insanely faster, pushed their cars to the limit, and then BOOM found out they were running too lean.

Yeah, running rich = wasteful and sooty. Running lean = too hot and deadly for engines.

So what could be causing me to run lean?

I've had a couple of mechanics mention a leak in the vacuum, or something like that... not sure what that means either....

it could be anything. O2 sensor could be the culprit but you would usually throw a CEL. a leak in the vacuum system could also be anything from a cracked hose to a hose being not connected at all. after months of running like crap (lean at low RPM and rich at high RPM) i found a hose that was not connected to anything. i called Kyle up and we compared motors. turns out the hose connecting the gas tank breather line/charcoal cannister to the throttle body was not connected. i turned the car on and placed my finger under the unconnected hole. sure enough my finger felt a little suction. i plugged the tube back up and i have actually gained ~10 more miles per tank, and the car doesnt feel errrrr hesitant anymore.