I read somewhere that the script originally had Biff "fading away" after returning to 2015. This was scrapped, as they thought that the audience may wonder why the car didn't fade away as well.

This plot hole has always bugged me, and affected my enjoyment of BTTF 2. I guess I must have an autistic streak.

Another bit of bad science I've just remembered is in "Lord of the Flies", something I actually commented on in my English lesson back when we read the book at school. If Piggy was short-sighted, his glasses would have concave lenses, and thus been useless for creating fire. William Golding, You Fail Physics Forever.