My car has somewhat of a similar issue. Upon startup (after waiting for glow plug relay to click) the engine shakes pretty hard and then kicks a few times and then smooths out. The idle upon startup is very close to 500 and then after warmed up completley it idles close to 800. I know I still have an air leak somewhere as there are those little tiny bubbles in the prefilter that build up after the engine has warmed up a bit (but dissapear after shutoff and cool down). I am ordering a new rack dampener pin and hopefully that will help. Then after the snow goes away in the spring Ill really get in there and start evaluating my fuel lines.

__________________
1983 300SD White with Grey interior