I have the same problem in my '93 and I will be installing new injectors tomorrow hopefully fixing this problem.

I also have white smoke at idle when cold and it runs really rough when cold.

When I give it some throttle it smooths out.

From some posts I've read on here the low pressure(?) situation that exists at idle will really expose worn/clogged injectors.

At higher RPMs the inefficiency of worn/clogged injectors is less obvious.

Somebody please chime in if I have given bad information.

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1993 W124 300D
-297K on the clock as I type this.