Time travel film title, from mid 1980's to about 1998?

[lee1958]

Here we go I need some help with this one please.....

A mid 80's to mid 90's low budget time travel film title

A guy in his 20's (somehow- fizzing light bulb in a bar?) ends up in the near future and comes around outside a bar, where we see his credit card(?) melting away. It's in a time where all plastic and petroleum products have been eaten away, due to a man made enzyme produced to help avert a major oil spill? He teams up with an old man and his young grandaughter, driving a horse drawn 1950's style Aluminum diner caravan.
Upon the the road he spots the shell of a 911 Porsche and the girl pipes up with a story " Grandfather said that once a upon a time you would actually drive across town to get a Pizza?
I dont remember much else that happened other than him trying to get back to his past. When he does and looks round he see's the figures carved into Mount Rushmoor and one of them is an Indian Chief!
So the film end's with a twist.

Your suggestions kindly received please

[Aquariel]

That is Doorways (1993):

http://www.imdb.com/t...tt0106752/plotsummary