about 3 weeks ago I had sought out biodiesel here on long island so that I could run a higher percentage than the 1 or 2 quarts that I was putting in the tank from my internet purchase of 5gals.
for years I have been trouble shooting this poor idle that I could not fix. I tried all the normal stuff that every one else would try,valve adj., replaced injectors, rack damper,timming chain, all filters, etc.
Well after my 11 gal fill up with the biodiesel I ran for about 300 miles until the next fill up which would not happen because of the temperture drop, my local supplier of biodiesel the fuel had jelled. off to the nearest station.
I filled up and went on my way, 2days later a power loss, just made it home and lucky for me I had spare filters, yup folks, it does clean very well, so well that the filter had clogged tight. after the filter change I drove around for a bunch of miles to see if everything was normal, it was'nt, it was actually better, the engine has not run this smooth in years and the idle has gotten so good that I think I am driving a different car.
After years of playing with everything possible to obtain the perfect idle, all it took was a tank full of biodiesel to clean everything spotless. I will continue to use power service at every fill up to keep everything normal between biodiesel use.
I share this info with everybody so hopefully some one else can solve problems such as I had, it seems to me that all these engines need is a really good internal cleaning to bring them to top performance

1984 300d 245k