Are you moving the car prior to washing it. I.e out of the garage or re positioning it on the drive. If so it is a simple case of flooding the engine with fuel. this happens to many modern cars if they are started and turned off to quickly. try running it for a few minutes before turning it off. Once flooded you can normally clear it by cranking the engine while holding the accelerator pedal right down. when the engine tries to start ease off on the accelerator. crank engine for 10-15 second bursts allowing the starter to cool down between attempts for about 30 seconds...