W203 Black smoke, bad idle

1)About couple months ago my MB w203 C220 CDI started dropping through exhaust a lot of black smokes, mostly of them on 700-3500Rpm's(kickdown). Maybe it could be an EGR valve or maybe something else? Where it is?
2)Another problem.. On the cold engine(idle), engine starts droping RPM's from 700 to about 500 RPM and it repeats about every 30-45 seconds.
Thanks a lot for answers!
Check the ducting from the turbo to the intercooler to the intake manifold for leaks, and the intercooler itself.
rgds
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But RPM's started dropping about two weeks ago..

