2005 x3 surging at 3200 rpm and moderate load

[seminoe]

While under ½ to ¾ throttle the car will surge and jerk especially in 3^rd gear at 3200rpm.  I have traced the problem down to short term fuel trim of bank 1.  As shown in the photos, bank 1 oscillates.  I have replaced both upstream 02 sensors.  I have swapped both downstream 02 sensors.  I have replaced all spark plugs.  I have swapped coil packs from bank1 with bank2 … no change.  I have replaced all fuel injectors. I have replaced the fuel filter in the tank. I have measured fuel pressure… typically about 50psi, but oscillates down to 45 psi during short term fuel oscillations.  I have checked the exhaust back pressure at each upstream o2 sensor.  The bad bank (bank 1) has slightly lower back pressure than the “good bank”. 

When the bank1 oscillations last long enough, the car will transition from closed loop to open loop.  When in open loop, the surging goes away.  

I have sprayed carb cleaner around the intake manifold while running looking for vacuum leaks… I have not found any leaks.

The car has about 130k miles on it.

The car seems to run fine unless you run at 3200 ish rpm under ¾ load.

[Bimmer Owners' Club]

would be worth measuring the exhaust emissions for oxygen content around the cruise speed range to see if there is excess O2 in the readings

 

[seminoe]

what would be the best way to do this? What does it mean if there is excess and what would then need to be adjusted? How is this different than the o2 graph that shows the actual o2 sensor output?

[Bimmer Owners' Club]

Measuring the oxygen can diagnose whether you have a vacuum leak on the inlet / air leak on the exhaust which could be the reason for the O2 sensor going out of range and the fuel trim dropping off due to the O2 sensor reading.

[seminoe]

Why is it ok except for a small RPM/load range? I have already sprayed the intake manifold and air tube box etc with carb cleaner to try and find a leak. Do not see any soot trails on the exhaust or smell exhaust.  How else would you look for a leak?  

Thanks for the suggestions.