I spend a few hundred trying to track down a vibration. Car was a bit out of tune so I had the carby looked at, was out of tune and the car did run better - but the vibration was still there. Got a new cap and rotor too, and reoiled my air filter... problem still existed (was pretty sure it wasn't any of this to start with but it needed doing regardless...)
Next was tailshaft balance, center bearing and unis. Almost $200 later, felt slightly better all round, but the vibration was just as bad as before.
Clutch needed doing too, so had this done. Problem solved! Car felt amazingly smooth (well, not Ecotec smooth but still a hell of a lot better). Clutch was rooted and a bit out of shape but the flywheel must've been warped to hell which would've contributed to the demise of the clutch, I'd say.
So - if it's a manual - get it sussed out. Don't know much on autos, but I've heard the flexplate can suffer similar warpage and will cause similar issues.
Good luck sorting it out
