Have them check the intermediate levers on the valve timing gear. That was a known issue for 2004 & 2005 X5's with the N62 engine (which includes the 4.8is), produced from 6/04 up to 2/05 production. Problem was technically fixed after that and for the 2006 model year, but you never know.

From the SIB: "Incorrect tolerances and geometry of Valvetronic intermediate levers are causing uneven cylinder filling during the transitional cold start period (60 seconds after the engine has been started) when the Valvetronic system is switching from the initial 6 mm to a minimum 0.3/0.8 mm valve lift."