Ok, I've asked a friend who works at volvo (15+years) as mechanic and he told me that he used to get a lot of cop cars in with the same symptoms as yours...the remedy was to basically change spark plugs and O2 sensor, and just check that all other stuff are ok (ignition coils, leads etc). Then take the car out for a very hard run...accelerate hard on as many gears as the road allows basically. This clears the buildup of all the carbon (swedish police are cruisers and rarely push the cars) which causes misfires etc. Also, you can actually see the the amount of carbon coming out when doing so.

It might sound unorthodox and sure it's not bmw but he has been successful every time with Audi, volvo and Saab.

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BMW X5 E53, 4.8iS - 2005
Professional Stereo/Nav with DSP (modified BM54 module) - Converted to Eonon GA5166X with Reverse cam
4-Corner Air Suspension - Converted to BC Coilovers