my nissan 2003 2.5s, started shaking. sometimes when I turn on the car , driving or at a stop. why? Nissan Altima 2.5s 4cyl. I was driving fine, tuned off the car to go into a store, when I turn it back on I began to shake and as I was backing up, I then parked the car, turn it off and waited for a few minutes, turned it back on and the car was fine. again, after running some errands, I started the car but this time when I turn it off and back on, it continued to shake, I drove off and later the shaking had stopped Later at a light the car begun to shake again.What could be the prob?