I just bought my first MB 300TD, 148kmi, after doing lots of investigating what type of diesel would run best on vegetable oil. Before converting, I want to get the thing running right and am now getting frustrated, I like the car a lot but wondering if I made a bad decision.

Starts good, and seems to run more smoothly when cold than warm. Once warm it runs rough (if it were a gas motor I would suspect a fouled plug). It has a lot of blow by and smoke in the valve cover (is this normal on this car???).....this scares me!!! so I checked compression, seems okay. The car lopes and vibrates a lot, at idle and even when I rev it to about 1500rpm. Also seems like it should have a bit more power, but I haven't driven many of these cars so not sure.
trying to solve the problem I have:
1. pulled injectors and had them tested, they tested okay
2. checked air cleaner (okay)
3. checked compression (hot) and every cylinder was over 300psi, ave. 315 and no more than 10psi dif. between them (it took about 8 seconds to get that high though)
4. adjusted valves
I plan to:
1. check timing chain stretch (just found out how to do that from this page)
2. give up, please help I am at wits end. From what I have read these are supposed to be great diesel motors, but right now I am wondering if I am in over my head......
thanks.
jb