I had a mystery misfire issue on my s53 4.4 that turned out to be a self destructing A compressor that the knock sensors heard and reported. If you can’t feel the misfires in the way the car runs you could have false misfires, but if you can feel them something is truely up.

Have you done a compression and leak down test on the engine?

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2013 X5 xDrive3.5i Premium
2002 530I Sport Package
2001 X5 4.4i
2001 M3