Good morning, Sara;
What you are most likely experiencing if you are getting a bad vibration when the car is running in gear is an engine misfire condition. Your engine has 4 cylinders into which fuel sprays and is exploded by the spark plug in that cylinder. The force of this exploding fuel as it burns is what creates power in the engine. If one or more of these cylinders is not doing it's share of the work, it will cause teh engine to run roughly.
There are many possible causes for this type of condition to occur. You could have an internal engine mechanical problem, you could have fuel not getting into one of the cylinders, or you could have a problem with the ignition system that is causing one of the spark plugs to not fire to ignite the fuel.
If the problem started rather suddenly, the most likely cause would be a spark plug not firing. Ignition system parts such as spark plugs and wires must be replaced every couple of years to keep the engine running smoothly; this is normal maintenance (Tune-Up). So, if you have not recently replaced the spark plugs and wires (also the distributor cap and ignition rotor) that would be a good place to start. Replace these tune-up parts with good quality new ones and it is likely that your engine will run smoothly again.
If the tune-up parts I mentioned above do not correct the problem, then you will need to take the vehicle in to your favorite local repair shop for diagnosis of the problem. Checking for internal engine mechanical problems and fuel system problems does require some special test equipment...
I have never known the Camry models to experience abnormal vibration issues; they are usually a very tight, comfortable vehicle with no noticeable driveline vibrations coming into the passenger compartment.
Was the vehicle like this when it was new, or is it a recent development?
Does the engine seem to be running roughly (you can usually tell if an engine is running smooth by listening to the exhaust at the tail pipe if you are not sure)
Is the roughness present only at idle in D , or does it also do this in P position? I'm trying to determine whether it is an engine misfire issue, or a vibration issue you are describing...
If the engine is not running smoothly at idle only, likely causes would include:
(1) Base idle speed below spec due to a faulty idle air control or throttle body depsoits restricting minimum airflow into the engine
(2) Camshaft timing slightly off due to a stretched timing belt
(3) slight valve leakage (a compression test and cylinder leakage test would be required to check for this condition).
Idle problems caused by any of these 3 things would result in a slight vibration at idle, but then disappear at higher engine RPMs.