Did these symptoms just start out of the blue, or was it a gradual degeneration in performance?
How did the plugs look when he pulled them?
What made him think that one O2 sensor was bad?
Are you using the correct grade of fuel/using a quality fuel?
You say it idles rough...what about when you accellerate/drive at a steady speed?

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It is a truism that almost any sect, cult, or religion will legislate its creed into law if it acquires the political power to do so. Robert A. Heinlein


09 Jetta TDI
1985 300D