OM617 Abnormal Idle

[Abe_Markillie]

My 1980 SD seems to idle good for one second, then rough and shaky, off and on while it's running. I notice it while doing the classic "mercedessource" vegetable oil mix clean. I plan to do a IP timing adjustment because I've heard it does wonders for these engines, and a good timing adjustment did a lot with my Ford 6.9 IDI. Does anyone have any input before I dive in? Maybe it's just a old fuel filter or something. It has brand new return lines and belts and such.