S8 Engine Problems Traced to Faulty Air Temp Sensor

I had very similar issues with my 2017 S7 4.0TFSI last year. Having some experience working on these engines, I first tried using a diagnostic tool to confirm the IAT sensor was the problem. The symptoms matched exactly, rough engine running, significant power loss, and persistent check engine light. The intake air temperature readings were clearly off, causing the engine management system to run rich. After confirming the issue, I had my workshop replace the air sensor. Total cost was 155 Euro including parts and labor. The repair took about an hour and completely resolved all symptoms. The engine ran smooth again right after the fix. To help provide more specific advice about your situation, could you share: Have you scanned for error codes? Are you noticing any additional symptoms? Has the fuel consumption increased? Does the problem get worse when the engine is hot? Engine issues like this can sometimes indicate other underlying problems, but in my case, it was just the IAT sensor. Getting proper diagnosis with a scanner is essential before proceeding with repairs.

Just had my 145000km service done last month, so the timing of this is frustrating. After reading your reply, I hooked up my car diagnostics tool and confirmed error code P0113, which points directly to the temperature sensor issue you described. Fuel consumption has jumped by about 15% and yes, symptoms definitely worsen when the engine gets hot. The engine becomes particularly rough after highway driving. The intake air readings are showing -40C consistently, which is clearly incorrect. One additional detail, there is a slight whistling noise from the front of the engine that was not present before. Could this indicate a vacuum leak affecting the air temperature readings?

Based on that whistling sound and the -40C reading, this is likely more than just a faulty IAT sensor. When I faced similar issues with my S7, I initially focused only on the sensor, but my mechanic discovered a small crack in the intake boot causing a vacuum leak, which explained the whistling. The car diagnostics showed P0113 in my case too, but the consistent -40C reading combined with the whistle suggests air is entering the system unmetered. The IAT sensor cant provide accurate air temperature readings with a vacuum leak present. The total repair ended up being around 450 Euro, more than just a sensor replacement because the intake boot needed replacement too. The good news is that fixing both issues completely resolved the rough running, restored normal power, and brought fuel consumption back to normal. Would strongly recommend checking the entire intake path for leaks before just replacing the sensor. A smoke test using proper diagnostic tools can quickly identify any vacuum leaks. This could save you from replacing parts unnecessarily. Since youre at 145000km, its also worth inspecting the rest of the intake system while its being worked on. These engines can develop similar issues around this mileage point.

Thanks for the detailed insights. After getting your feedback and investigating further, I finally scheduled the repair. The car diagnostics confirmed exactly what you described, both a failing intake air temperature sensor and a vacuum leak. The -40C readings and whistling noise match the symptoms you encountered with your S7. The mechanic has ordered both the IAT sensor and a new intake boot to fix all the engine issues at once. Total quoted repair cost is 475 Euro, which seems fair based on your experience. They will also inspect the entire intake system given the mileage, which makes sense to prevent future problems. Really appreciate the tip about the vacuum leak, would have likely just replaced the sensor and still had issues. Will update once the repair is complete, but feeling confident this will resolve the rough running and power loss issues completely.