Did you get any codes? I did conversion and it is over 24k miles with no issues!
In my case, when vacuum plug in the side of the intake manifold developed small crack, I got fuel trim codes. Check your fuel trims and inspect those two hard to reach small vacuum plugs on the side of the manifold.

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2012 X5 x35i My new toy
2005 X5 4.4 Her's (Retrofitted Servotronic Steering Rack)
2003 X5 3.0 Mine (Retrofitted Servotronic Steering Rack and Heated Steering Wheel)
2001 M5 Son's car
2000 540i 6sp Sports pkg, supercharged. Son's car (Sold)
2001 530i (Sold)
1999 528i (Sold)
1975 2002 (Sold)