It could be your motor mounts (usually always slightly vibrating the car, especially when accelerating) or most likely not aligned/damaged driveshaft on rear wheel drive vehicles.
check the idle speed with the car in gear, if it has a tac on the dash it should idle in gear at about 700 rpm if its too low the car will vibrate or stall.
Probably the alternator or its drive belt has failed
There are many reasons why your car might vibrate while it is idling. It could be running too hard for example.
Yes, well I can do it on my car
If you continue to drive your car while the timing is off,your motor will start to act a little funny.I would NOT suggest you continously drive your car like that.
Not all Altima's vibrate. If the car is vibrating, it may mean that there is something wrong with the tires.
to drive slowly
To test drive a car means to take a car for a drive and see if you like the way it handles the road or just to see if you like the car :)
Ask someone else to drive the car while you rest in the passenger seat.
If you have a 4-wheel drive car it shouldn't be in 4-wheel drive but if you accidentally or knock it into 4-wheel drive you have a gear leaver like item at the side of your actual gear stick. It will be vibrating a bit but that's perfectly normal. If your 4-wheel stick is up then its in 4-wheel drive but if its down your not in 4-wheel drive.