I have a 1983 Mercedes 240D with a 4spd, (manual). My engine has 24,000 original miles on it. It was purchased as a factory crate motor from MBNA and came complete with everything including the injection pump, etc...

Recently I have begun to notice that after my engine warms up, it idles poorly. Slightly revving the engine makes it worse. It shakes and misses terribly. However, above 1,400 RPM it runs smooth as silk.

I adjusted the valves to factory spec and replaced the fuel filters. No difference. The engine has plenty of power with no smoke. At highway speeds, engine appears to run perfectly.

One other observation, which happened by accident when a friend gave a 5 gallon jug of veggi oil to try in my benz, is that if I run thicker fuel, like vegetable oil, the problem completely goes away. but if I go back to diesel, the poor performace at low RPM comes back.

My conclusion is that my poor idle is the result of timing chain stretch which caused a slight change in IP timing, something I would have expected since the most chain stretch occurs within the first 20 to 30 thousand miles of an engine's life. I am guessing that the thicker fuel (vegetable oil) ignites more slowly than the diesel and my timing being off is compensated by the delayed ignition of the thicker fuel, (veggi oil).

So what I would like to do is test and adjust my injection pump timing. I did a search on IP pump timing and came up with all sorts of buzz words like "drip method", "well method", "milli volt", "RIV", "woodruff key", "RD bolt" and even "give the IP a slight bump toward the block"

What I would like to know is:

1. What is the best way to test my injection pump timing, (assuming I need to do this)
and
2. How do I go about adjusting the IP timing so it runs better on diesel? Is there a way to adjust the IP timing while the engine is running so I can get a feel for where my engine idles best? Can I do this, or is not advisable?

I really appreciate your help and advice. You guys are great! Thanks!