MITSHUBISHI LANCER is 2002

Hello everyone, I wanted my problem with my car and seeing if they can give me a hand, the problem of my lancer is that when I carry it in D it works normal and when I will always be moving, suddenly it goes out but it is not followed it happens to me when you see when, my question is that it will be what causes it to turn it out in n and the car in the move
?
In case you can give me a hand I would appreciate it very much.
thank you.