Slight Stumble at Low RPMs and Poor MPG - Many Things Replaced

[rollinn95z]

Howdy and thanks for your time.

Newb here, but I am at the end of my rope. Have had an X3 for a decade which has treated me decent and decided to jump into a 2011 X5 35i N55 (2010 build) last summer with 50k from a BMW dealer in Florida.

Ever since I got it back to NC it has had a slight stumble/shudder at low RPM under load like when sitting stopped in gear at a light. It's temperature independent and more noticeable on initial startup. It has manifested further as bad fuel economy, barely 13-14 city and 15-16 highway. Most commonly would be classified and feel like an intake air leak or fouled plugs at the verge of stalling, but the intake system has been smoked twice with no leaks found.

Only at one point over the last year has it thrown a CEL which I believe was a P00BD "Mass or Volume Air Flow 'A' Circuit Range/Performance - Air Flow Too High". That prompted the replacement of the turbo as it was leaking oil and blowing a lot of smoke on start up. After having been pulled, the turbo impeller does have slop both along the longitudinal and rotational axis.

I've had the dealer, my independent, and a local German tuner shop look at it. I trust them all within reason and the dealer even sent a data set to the factory engineer to investigate. No one has definitively nailed this down.

The following parts have been replaced over the last year by the dealer, the indy, or myself in the following order:

ECM updates, plugs, vanos solenoids, fuel injectors, HPFP, coils, valve cover and gasket (leaking), water pump (failing) and thermostat, walnut blast intake ports, rear main seal (leaking), oil pan gasket (leaking), turbo (leaking at mid clamp), and most recently upstream O2 sensor.

Neither the MAF or MAP sensors have been replaced. When the oil pan was dropped, they discovered 3 sheared bolt heads and 2 sheared bolt threaded bodies originally from the front face of the vanos unit. That was "repaired" early in the life of the X5 with a recall, was double checked 2 years later, and most recently my indy checked that the vanos still had the bolts intact. The dealer never pulled the pan with the initial recall.

So, I've thrown a metric f-ton of cash at this thing and was ready to punt just before the CEL and turbo replacement. It has no current CEL; so remaining speculation could be a rogue sensor, clogged cat, tweaked vanos, or eccentric shaft gone out of tolerance.

Anybody want to hypothesize a cause or can refer a phenomenal BMW wizard in NC, SC, or southern VA?

Thanks and I appreciate the input!

-MJ