I'd take the engine apart and see what happened. Sounds like a sensor failure or a big vacuum leak. Scan it with an ODBII reader if possible and let us know if you find any codes— that might clue us in on what happened with your engine.

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2003 X5 4.6 | 2000 540i Touring

Formerly owned:
2004 Range Rover | 2000 M5 | 2000 540i/6
1995 750il | 2003 Mercedes S500 | 2003 540i/6