It's also possible that the high bio blend was clogging the particulate filter. I don't know exactly how MB designed the filter purging to work, but I've heard that VW injects extra fuel every now and then to purge the filter and this only works when you're burning fuel that burns exactly like diesel. Bio has lower volatility and slightly higher viscosity than diesel.

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2004 VW Jetta TDI (manual)

Past MB's: '96 E300D, '83 240D, '82 300D, '87 300D, '87 420SEL