I did accidentally find one way to save them. I'm playing the neighborhood, most houses, so if a car is near a house, type in testingcheatsenabled true (after cntrl shft C) then enter, then bring up another cheat box cntrl shft c and type in moveobjects on and then make sure you're in the build mode and move the camera out so the car is in view cntrl shift on the car and another option comes up to reset it (normally it's just a delete). I reset other sims cars that were in front of the sims house that I was playing on. I've done it a few times now. This assumes they have a parking space (all my homes do, even the ones in the city, ROOFTOP parking for 2 families). And of course turn the cheats off after this is done.