Just a guess but it might be the DME unit (the brains of the engine--controls every calculation in the engine). I had mine replaced luckily in April 2016 (there is an 8 year warranty on them from BMW). The failure rate on those is really, really low though--like 1 car in 300 they go bad.

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2008 X5 4.8
Jet Black/Black Nevada/Dark Burl Walnut
Adaptive Drive
Premium Pack
Tech Pack
Climate Pack
Sport Pack
20" Wheel Option
Premium Sound
Sirius Satellite
Rear DVD Entertainment
Multi-Contour Seats
Comfort Access
3rd Row Seat
Heated Front Seats
Running Boards
3M VentureShield Paint Protection Film