Most likely cause for a P0171 Code with M62 V8?

[BimmerM3inGA]

I've had my 2002 4.6is (108K miles) for a couple of months now and have been patiently sorting it out. Thankfully it hasn't really needed all that much - just a lot of little stuff. And maybe a couple of big ones…

So I thought I had it pretty much straightened out until I was driving it today and the check engine light came on. Great, now what! I just read the codes with my cheap little handheld code reader because the battery in the laptop I use for DIS/INPA is dead and my only extension cord is in use charging the battery in the old M3. I know, first world problems.

Anyway, this is the code I'm getting:

P0171 Cnf Mod11, Bank 1 System Too Lean

Experience tells me this is most likely a vacuum leak. And if were on an M52/52TÜ/54 I'd immediately suspect the oil separator/crankcase vent because 99% of the time, that is the source of the leak. Is there an equally likely source on the M62 V8? I'd like to know what the most likely culprit is before I order a bunch of parts and do a ton of work that it may or may not need.

I've been doing some snooping around and have seen a couple of potential problem areas, but nothing conclusive. How have others resolved this?