Low compression could also be the cause as could bad injectors. I think a compression check would be a good idea. This way you or your mechanic can also pop test the injectors as those are often pulled out for a compression test. You don't have any gasoline in your tank do you? :p

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2004 VW Jetta TDI (manual)

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