I just thought I would post a quick update. I took my 01 X5 4.4i to a local indy shop and they ran a smoke test and told me that my MAF sensor was bad and that the coolant leak was because my valley pan is cracked. They wanted something like $520 to get me a new MAF installed! I thought that was crazy!

Well, if anyone was wanting to know a cheap option to the BMW MAF, I found a brand new MAF on ebay and it did the trick! After one day of driving with my new MAF, the SES light went off and now the thing has power again...Huge difference. Alltogether, with shipping, the MAF cost me $72 vs. $489 from dealership. Awesome!

I have an 01 4.4 with 126k and yes a bad MAF will cause a lean bank condition on 1 or 2 sometimes both, typically there might be a couple things going on like a bad vacuum hose to complicate things. I was able to get away by cleaning mine a couple times, but it finally died on a trip to the mountains...luckily found a BMW dealer and they had one in stock, $400, asked to borrow a screwdriver and installed it myself in 5 min in parking lot with SA & parts guy watching, guess they don't see that very often!

Bought one on ebay too, but it was worse than my old one, just trash, you were lucky.