Check for vac leaks on the top manifold that causing uneven revving normally revving up though, as for low take the throttle body off and give it a dam good clean with carb clean !
If its vibrating and juddering sounds like it has a bit of a misfire ! They run a little rough and when I bought mine that's what I thought, but after a Friend got I'm and said it was a bit too bad I sorted it , ended up putting a coil pack, leads and plugs to make sure !
It drives loads better now , and it's really not that rough idle now !