Could be a number of things - rough running because it needs a tuneup, or maybe a vacuum leak. Bad/broken engine mounts will exacerbate the feeling. (I consider mounts to be a normal replacement item, every 5 years or so.)

Start with checking plugs, plug wires, distributor cap and rotor. If those are ok, look for vacuum leaks in all vacuum lines and also the big snorkel between the AMM and throttle body - these develop cracks, especially on the underside.

One other place to look for vacuum leaks is around the injectors and also the intake manifold gasket. Get a can of spray carb cleaner with the skinny red extension tube. With the engine idling, spray the stuff along the manifold/head interface, and then around each injector. If you get a momentary change in idle speed/roughness, you've found the leak.