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egine rough at idle.

Started by Rob Smith, 21 May 2022, 04:43 PM

Rob Smith

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.


s class

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.

[color=blue]'76 6.9 Euro[/color], [color=red]'78 6.9 AMG[/color], '80 280SE, [color=brown]'74 350SE[/color], [color=black]'82 500SEL euro full hydro, '83 500SEL euro full hydro [/color], '81 500SL

Jay Gibbs

Could be gummed up injectors too. My 75 450SL had d-jet morning sickness. Removed the injectors and sent them off to Witch Hunter for testing and cleaning. Cost was less than $200.00 with very good results. Also helpful was slightly leaning at ECU. Combination of results was an overall smoother running engine as well as going from 8mpg to 12...



Is there a thread related to leaning the injectors at the ecu? I've just got my injectors reconditioned this might help get it running