Injection timing on these diesels rarely needs adjustment as long as the timing chain isn't stretched. Lots of blue smoke indicates either unburned diesel fuel or if it's thick blue smoke it's oil getting into the combustion chamber. Most likely it's the former. Did you check your glow plugs and are you letting them stay on for at least 15 seconds before starting the engine? Have you checked your injectors for spray pattern and pop pressure? If that all checks out, you should run a compression test. Then I'd mess with the injection timing.

I don't believe the IP oil is to be changed on your model.

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2004 VW Jetta TDI (manual)

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