Scene: Man driving convertible singing old song. He was on a Sunday drive by himself, open road…he was driving slow, swerving back and fourth, road was lined with trees….it may have been an old foo-wop song...

Sounds like a scene from Road House - Road House (1989) - IMDb (http://www.imdb.com/title/tt0098206/)

The song was Sha-Boom.
Road House (1989) Sh-Boom - YouTube (http://www.youtube.com/watch?v=xLdyuwqik4Q&feature=related)