Peter,
not likely the plugs; all new 6 months ago, had the problem before and after.
I have some Purge on the way.
Could very easily be air. I know my lines are old and a little leaky.
Will keep you updated.

__________________
Paul
2004 E500 4matic; 72,000mi

This might be the solution for the rough idle on 87 300D. It is called three-phase glow plug control.

For more information visit

www.beru.com/english/produkte/gluehkerzen/dreiphasen.php

If somebody has any experience with this glow plug controller please give us your opinion.