Does it idle ok when started? Check your choke but to me might well be a maf. With ignition off undo the maf sensor and try driving it from the same situation... If it accelerates fine then its ur maf. Wont be the Vanos i dnt think because the vanos doesnt kick in till 2000rpm. If the car feels like its slipping, u may need to top up/ replace ur transmission fluid. Might well be ur torque converter hasnt enough fluid in it. Last but not least you may be developIng either a dodgy crankshaft or cam sensor. If you car stalls, struggles to start, or feels like its in a Limp mode, it could be either one.