21% is pretty bad. We really can't complain about the emissions programs treatment of diesels, it's a lot rougher on the gas engined cars. Anyway, valve adjustment, air filter and try it again to see if there is an improvement. If you are close to Ellington I'll take a look at it for you.

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83 M-B 300D- daily driver
83 240D gray market
2002 VW Jetta TDI- beater