Run straight diesel from your purge setup and see if it smoothes out like it does on the purge. If it does, you know it's an air problem (time for new rubber fuel lines and clamps), if it doesn't, you know it's injector issues or compression problems.

__________________
Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]