You might as well get it done. You got this far already.

I really can't think of anything else.

Thanks man - I really appreciate you pondering on this along with me. It's been a LONG battle with this prob. My original indy and BMW couldn't figure it out without wanting to take the shotgun approach and throw parts at it. I have a new indy now and hopefully if I get desperate enough, I'll take it to them. With the amount of bimmers this guy turns around and his return customer satisfaction, I have a feeling he'll figure it out.

hey, i am having the same issue as you do this time. and i cant figure out what's wrong, did you have urs solved?
i have 06 x5 3.0I
my first engine check light was bank 2 running lean, bad o2 sensor(upper stream bank 2), this diagnose and repair was all done by dealership($600 parts and labor), i replaced bank 1 upper stream o2 sensor myself afterward. figured it out it may go bad soon.

second time engine check light was bank 1 running lean. i had found that the intake elbow boot had a leak, so i had it replaced. problem solved.

last month i tried to start my engine, it ran very rough and was shaking really bad, engine check light came right on, it was the spark plugs, i had them replaced, and the light cleared(it was misfire), the old plugs came out to be very dirty.

the light came on again after few weeks i changed my plugs, it calls Catalyst Fuel Trim Too Rich Bank 2.
i checked all coils they work fine. checked intake runner valve, it has decent resistant when i was trying to flap. my next checking list will be fuel injectors, down stream o2 sensors, fuel filter and MAF. do you think my cat got damaged due to the bad plugs?

For me the solution was the Crankcase Vent Valve. I replaced it but the replacement was defective. It also melted one of my O2 sensors.