That is weird. You can verify this on your own car. With your head over the engine compartment, rev the engine slightly past 1000 RPM than back down gradually to idle. You should hear the 3/6 valve close audibly if it's like my car.

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2004 VW Jetta TDI (manual)

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