You mean like, a wind turbine attached TO the car? So that it generates electricity or angular momentum or something to then power the car?
It won't work because said devices require work to operate. That work has to come from somewhere, and while the vehicle is moving it's coming from the engine of the vehicle, effectively making the whole idea pointless. Not only that, but every time you transfer energy into another form (wind to electrical in this case) you lose some of that energy to heat.
If it was only deployed when the car was stationary, it would take work to deploy it, since you don't want it running while you are moving due to the above reasons. Plus, the wind at the altitude of typical car travel is negligible, and the size and efficiency of the turbine required to make any small use of this idea would be enormous and costly.