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Same problem on my 2.5 TDI. Changed the airflow meter, but did not get to the root of the problem.

I do not get sufficient boost. On a drive test, maximum was about 1600 mbar, while air flow was about 650 mg. This was in 5th, at 4000+ rpms. However, my mechanic says that I should be getting 2000 mbar and over 1000 mg in 3rd, at 3000 rpms. I don't even approach these values.

Occasionally, the turbo bypass valve would block open, in which case I totally lose boost pressure, and car runs like ****, having no power and topping at 2000-2500 rpms. Tested while car is sitting, the valve seems OK.

Next, I thought that the catalyst was clogged (had a major oil consumption problem before). So I tried cleaning it, but I noticed no improvement.

Another strange thing is that engine temperature usually stands at 78 degrees Celsius. Only when accelerating hard (as hard as the car would let me) up to 180 km/h it goes up to 90 degrees. This is not normal. Could the two problems be related?

I am now thinking of testing and adjusting the injection timing. If that does not cure it, then maybe I'll change the bypass valve. I have no other ideas.
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