So I've had the X5 for a year now. A few months after I got it, it threw a CEL P0174. I posted about it, it did clean up and go away after some seafoam.
A little while later I started to get an oil burning smell accompanied by a P0174. I looked into it and it was a bad valve cover gasket. It was crystalized onto the valve cover and was letting oil drip down in the spark plugs. New gasket, new cover, smell goes away as does the CEL.
I looked into why this happened, and as suspected, it's the CCV system. It gets clogged, you get excess pressure, you blow a gasket. I replaced the CCV system, but suspected the gasket may have blown again.
About a month after finishing the CCV system​, I get the oil burning smell and CEL again, same code. So I order a new gasket and replace it. Clean spark plugs, clean connectors on coil packs, use maf cleaner and a rag to clean oil out of spark plug holes. Check oil, it's burned about a quart since I did an oil change after CCV reppacement. Top it off. CEL is gone, but smell is still there. I'm thinking it's just excess that needs to burn off. Now CEL comes back on later this week.
And that brings me to here. Still getting the CEL, still an obnoxious oil burning smell. No real hit on performance.
I havd torque pro running on my Android deck with the Bluetooth OBD2 adapter. I have it setup to monitor vacuum, temp, air temp, fuel trim, o2 voltage on all 4 sensors, maf throughput, and engine load.
Nothing out of the ordinary is happening at idle or while driving. Sensors on bank 1 are pretty much identical to bank 2. The code is a bank 2 error. Prior to redoing the valve cover gasket, I was getting P0173 and P0174, both banks lean. This lead me to the vacuum leak, aka valve cover gasket blown. They both cleared by themselves after replacing it, but P0174 is back.
Also to note, the second spark plug in was the one most affected by oil, but that's thd front and I believe that's bank 1.
Any ideas?

TLDR:
P0173 AND P0174. Replaced CCV and Valve cover gasket. Oil burning smell still and P0174.

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2006 X5 3.0i
2000 323i R.I.P.