Definitely unburnt atomized fuel from your description.

Maybe the IP was installed out of phase.
Surprisingly these engines can run, albeit poorly, when the IP is timed to the wrong compression event (exhaust instead of intake).

__________________
78 W116 300SD 'Desert Rose' new as of 01/26/2014
79 W116 300SD 'Stormcloud' RIP 04/11/2022