Diesels, generally, can idle roughly for several reasons most of which
involve combustion efficiency.
A diesel is usually a bit rough when cold - no matter what. So temper
your expectations, it's not a gas engine.
If it's rough because of misfiring the first suggestion is that a glow
plug needs to be replaced. They can be individually checked for
continuity with an ohm meter or one can say "if one's bad today another
may go bad tomorrow" and replace all of them and be done with it. If you
need to replace any buy only Bosch or Beru replacements.
The next thought is carbon build up on the injection nozzles. Try adding
a few cans of diesel injector cleaner to the fuel; it may cure it.
Alternatively one can remove the nozzles and have them professionally
cleaned and calibrated by a diesel shop.
There's probably an idle stop adjustment on the injection pump. (By
"stop" I mean a set screw that limits the travel of the lever that
controls the engine speed.) This is a "permanent" type of adjustment
made with a screw driver and a wrench for its lock nut. So go slow if
you undertake this - adjust ONE turn and lock it - drive for a few days
and adjust again if needed.
Finally, the engine's valves, if mechanically adjusted, may need to be
adjusted. Your engine may have hydraulically (automatically) adjusted
valves, I don't know; you need to find out and act if they're mechanical
for unadjusted valves lose compression, and that causes hard starting,
poor idle and reduced power. Rough idle is the first symptom.
After the engine is set to specification but the car has too much
vibration, the motor's rubber mounts ought to be checked and possibly
replaced for (your) comfort.
Hope this helps you.