I disabled the EGR on my OM611 car (same engine, only 4 cylinders) and it took ages to get warm from a cold start, and the MPGS actually went down.

I can believe that. I have read that the EGR system on the CDIs assists in warming the engine to operating temp. I note my CDI has reduced MPG during the warm up process according to the on board computer. Anything that would make the process longer, like lack of an EGR valve, would cut into fuel mileage.

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-- Chris

'95 E300, 216k miles, Silver Surfer
'05 E320 CDI, 138k miles
'07 S550 4matic, 69k miles

Gone but not forgotten:

'76 300D, 350k miles?, SOLD in 1995
'75 240D, 300k miles, SOLD in 1991

While I'm not generally a fan of additives, I decided to continue the Opti-lube regimen (boosts cetane and lubricity) that the PO used for the last 100k miles. It's cheap, it can only help, and one of the ways I suspect it will help is cleaner intake, EGR, etc....

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14 E250 Bluetec 4Matic "Sinclair", Palladium Silver on Black, 160k miles
06 E320 CDI "Rutherford", Black on Tan, 179k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver on Tan, 145k mi, wastegate conversion, ALDA delete

19 Honda CR-V EX 79k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife