Skip,

I believe the time frame your car was manufactured in was a period when MB had a problem with the Viton material used for the valve stem seals. I know it was such a problem on 190E's of that time frame they were replaced regularly, free of charge, even after the warranty expired. When these things fail, they can let engine oil enter the intake manifold whenever it is below atmospheric pressure.

In a turbo Diesel intake vacuum only occurs when you are idling and starting. This is inconsistent, however, with your report that you are not burning any oil. Smoking and missing at idle, following a "cold iron" start and assuming you spend most of the time with engine running with the engine under load (not idling), will not consume that much oil yet show a plume as the engine combustion temperatures are lower then and incomplete combustion of the Diesel fuel is common. So any added engine oil will also be unlikely to burn completely, and a Diesel at idle warms up very slowly compared to under load, so leaving it idling after a cold start will show the problem longer (and consume more oil).

Enough oil leaking into the intake manifold to cause a bit of blue smoke at start up can also develop a carbon build up on the intake valves that will interfere with proper valve function. This can lead to other problems like poor valve seating and lower compression, that show as poor starting, rough running as well.

Almost any other form of degradation of the combustion characteristics is cured by new injectors, valve adjustment or an "Italian tune-up." In some cases the prechambers can be damaged or clogged with soot from bad fuel/combustion and require replacement. Problems that have advanced to the point of damaging the prechamber ball pin, or clogged the vent holes show more extensive running problems (don't go away when you get beyond idle speed).

So, maybe you need to have your mechanic take a look inside the intake manifold and view the back side of the valve poppets and stems. If he changed the injectors he should have shined a flashlight in the hole and performed a visual examination of the condition of the prechamber ball pin, and anything else that is visible. Other than that, I cannot offer much of a suggestion. Good luck and I hope this helps, Jim

__________________
Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)