Audi S4 Boost Issues: Sensor vs. Intake System Problem

Had a very similar issue with my 2013 Audi S5. At first, I thought it was a major problem because of the power loss and those concerning noises, but it turned out to be relatively straightforward to fix. With some experience working on Audis, I recognized these symptoms. The temperature sensor in the air intake was indeed the culprit, but not the sensor itself. The workshop found a loose connection where the wiring harness connects to the temperature gauge sensor. The cable had worked itself loose over time, causing inconsistent temperature readings and making the engine run in safe mode. Total repair cost was 95 Euro, mainly labor for testing and securing the connection properly. Much better than replacing the entire temperature sensor unit. To help diagnose your case more precisely, could you share: Current mileage on your S4, Whether the temperature fluctuations show up on your scan tool, If the whistling noise changes with engine RPM, Whether the issues started suddenly or developed gradually These details would help determine if your case matches what I experienced or points to something else in the air intake system.

Last service was at 155000 KM, so pretty recent. The temperature fluctuations definitely show on my scan tool, ranging from -10 to +40 out of nowhere while driving. The whistling noise gets louder with higher RPM. The airflow sensor readings also seem erratic, which might be related to the temperature sensor issue. I tracked the noise to the air intake area, and it seems most prominent near where the charge sensor is located. Really hoping its just a wiring issue like you had. The fact that the problem started gradually over a few weeks makes me think its not a sudden failure of a major component.

The gradual onset and symptoms you describe match my experience exactly. When I faced this on my S5, the erratic temperature readings from -10 to +40 were nearly identical. The connection issue I mentioned earlier caused similar inconsistent readings in the airflow sensor data too, as both sensors share part of the same wiring harness in our models. Based on your description of the noise location and the gradually worsening symptoms, I am even more convinced you are dealing with the same electrical connection problem I had. The charge sensor wiring tends to work loose due to engine vibration over time, especially around the 150000 KM mark. One quick check you can do: gently wiggle the wiring near the charge temperature sensor while the engine is idling. If you notice the readings fluctuate more during this test, it further confirms the loose connection theory. For reference, after my repair: Temperature readings stabilized, Engine power returned to normal, The whistling noise disappeared completely, Both temperature gauge and airflow sensor readings normalized The fact that your last service was recent might mean this issue developed just after they worked in that area. Worth mentioning this timing when you take it in for repair.

The gradual development of the issue definitely makes your wiring harness theory seem likely. Thanks for sharing such detailed info about your experience, the matching temperature fluctuation ranges are particularly telling. I feel much more confident now that this might be a straightforward fix rather than a major system failure. Will try that wiring wiggle test you suggested before taking it to the shop. Since my symptoms align so closely with what you experienced, the location of the whistling, the charge sensor readings, and the gradual onset, I will specifically ask them to check the wiring connections first. The timing relative to my recent service is a good point too. I recall they did some work near the air intake system during the service, so its possible something got disturbed then. With the temperature gauge and air sensor data matching your case so closely, I am hopeful this will be a simple repair rather than needing to replace any major components. Will update once I get it checked out, but based on the similarities to your situation, I am much less worried now about potential major issues with the air intake system.