So to close the loop on this, I replaced the gaskets, checked the hoses. The vent hoses both looked good but the smaller oil return hose that connects under the manifold was in bad shaped and simply pulled apart when I detached it from the CVV. I couldn't get to the shorter oil return host that connects to the bottom of the oil separator, but as best I could tell, it was in OK shape.

After I buttoned everything back and cleared the codes again, the P0171 came back... but then I got the P0174 code too which I wasn't getting before. I was a bit worried that I'd missed something or screwed the car up worse, but I decided after reading in another thread that the MAFs are the same in the 4.4 engines as well as the M5 that I'd swap in one of the MAFs from my M5, clear the codes and see how it goes.

Well, no codes, I passed emissions and OMG was the X5 down own power! I never noticed because my daily driver is an M5 and I figured with the smaller engine and a lot more weight... the X5 was just a pig but holy cow!

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Matt Atkins
'01 Titanium Silver X5 4.4
'01 Lemans Blue M5