Have replaced brake booster supply line, oil, air & fuel filter's, most vacuum lines, injector return lines, rebuilt vacuum pump (oh joy), replaced all belts, cleaned ALDA valve banjo's, ran diesel purge & run high octane injector cleaner every other tank. Getting ready to adjust valves, replace injector nozzles, replace the intake seal rings & transmission vacuum valve levers - all in hopes of curing the rough (shimmy & shaking) idle and blue smoke that come on out of the blue (one day purring like a kitten, next all heck broke loose) and by the way motor mounts all look good. Any thoughts on if I'm headed down the right path or ideas as to what I might be missing!!! All constructive comments most appreciated!!!
Forgot to mention car has 196,000 miles on it. Bought 22 months ago from man who had stored in a barn for 7 years. Has been running great for 21 months, then all of a sudden not so good.

One cause of blue smoke you don't mention is failing turbo oil seals.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13