Try blocking off the EGR valve, or at least check its operation. My first MB was a 123.190 (non-turbo wagon, OM617 motor) was an absolute dog with lots of white smoke that smelled of diesel and it could barely go 50 mph. I tried everything I could think of: new filters for air and fuel, set the valves and set them again, replaced all the injectors. Engine ran smoothly with no missing, just miserable power and too much smoke. Finally I blocked off the EGR, and I instantly had a new car. Top speed (only explored once) was an indicated 110 mph. I was SOOO happy! The EGR had failed in the full open position, effectively choking the engine on its own exhaust and cutting off most of the oxygen.

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Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC