I'm having an issue with my 1973 450se. When started cold, idle is really rough sounds like a few plugs not firing and #4 and #8 plugs sooty. The temp gauge is erratic and doesn't seem to move any. I haven't let it warm up because it's too rough. Any help would be appreciated.
Djet is notorious for running rich when cold, which leads to the fouled plugs. You can try leaning it out a bit at the ecu and/or mps. You could also try going one heat range up on the spark plugs. A contributor often is a tired AAV that isn't giving enough additional idle air when cold.