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2012 Audi A4 2.0T Premium 4dr Avant Wagon Auto quattro

2012 Audi A4
Trim Info:
All-Wheel Drive, 4 Door Wagon, Small Station Wgn
21 (2011) mpg city / 27 (2011) mpg hwy
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February 12, 2013, 8:58 pm

Luc V

Question: Boost pressure...

I have the K03 OEM turbo, all the car is original (no mods at all) except I have installed a boost gauge about 2 months ago.

I have had some noise issues coming from under the hood (hissing sound when cruising at whatever speed) when it's cold outside. This started way before I had the gauge installed, it started in winter 2011-2012.

Now that I have a boost gauge, I noticed that the turbo doesn't hold it's boost like it's supposed to (supposed to hold at 8-11 PSI from 2500 to 5000 RPM). It gets up to 10-11 PSI but drops to 4-5 PSI before hitting the 4000 RPM range.

I'm thinking that the hissing sound and the boost problem could be linked, has in a faulty or worn out diverter valve or something similar.

I have also poor gas mileage... A friend with the same car (all stock too) gets up to 500 miles with a full tank but I get only 350-400 miles.

I want to fix this before applying a stage 1 APR/Unitronic chip tune to get a bit more "Umph" from the 1.8T...

Would like to know your thoughts about this??

Thank you

February 16, 2013, 3:14 pm

Ron W
Expert Mechanic

The hissing is probably a vacuum/boost leak somewhere in the intake system. And if it has too much air, fuel trim will be on the rich side which will effect fuel economy. This also makes sense if you are not getting the correct boost pressures.

You should have the intake system smoke checked. This will find any leaks that could be causing these issues.

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