Last tuesday South San Francisco was near freezing, i live on a hill so it was freezing . I was worried for morning because my SD was at 1/4 fuel level and it was B100! So i cycle the glow plugs longer and start it, it stumbled, shook, rattled but it was running.

So off i went to work. Im low on bio (need to re-order some) so i filled up on ULSD at chevron. And i started noticing after a longish drive my car idles like it has low compression on some cylinders but runs just fine when moving. Today i filled up at the biofuel oasis in berkley on my up to vallejo to pick up a friends car. On bio i noticed the car idles normally and not like its low on compression. And still runs just fine.

Why is this? Im due for valve adjsutments and have been putting it off as ive been way to busy to do it but could this be a cause? If so why does it idle weird on ULSD and not on bio?

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Current:
05 E320 CDI
07 GL320 CDI
08 Sprinter
05 Dodge Cummins
01 Dodge Cummins

Previous
2004 E55 AMG
2002 C32 AMG (#2)
1995 E300
1978 300D
1987 300D
2002 C32 AMG(blown motor :[
1981 300SD
1983 300SD
1987 300SDL
2002 Jetta TDI
1996 S420
1995 S500
1993 190E 2.6
1992 190E 2.3
1985 190E 2.3 5-Speed