UPDATE
I haven't figure it out yet but today it developed a new problem. As I said before, the car drives fine and does this shit only in reverse. Now, if I move let's say on 3rd gear, 5000rpm and go full throttle, and let it go suddenly, it shuts off for a split second and turns on again. For a single second while the engine moves when I let off the gas. This gives me the impression that when the engine moves forward something it gets disconnected or whatever. Any ideas?