Actually I finally clicked through to the link you shared (
) and saw the image of the flying car and it looks so similar to the car I had in mind that it just may be the same one!
It's entirely possible that the TV show I saw was about multiple prototype cars, some of which could fly, some of which could be driven into the water, and my memory somehow combined them into a single car that could do all three.
So you weren't useless at all. My memory was!