Audi Q8 Turbo Troubles: Whistling Sound & Power Loss

I had a very similar issue with my 2018 Audi Q7 diesel last year. Having some experience with turbo-related problems, I recognized the symptoms immediately, especially that characteristic whistling sound during acceleration. The main problem turned out to be a defective electrical bypass valve affecting the entire boost pressure control system. The pressure sensor readings were all over the place, causing irregular boost pressure and the exact symptoms you describe, weak power delivery, increased fuel consumption, and unstable idle. After proper diagnosis, the workshop found that the actuator valve was failing to regulate boost pressure correctly. The complete repair, including parts and labor, cost me 250 Euro. The fix restored normal boost control and eliminated all symptoms. For a more accurate comparison to help with your case, could you share: Current mileage on your Q8, When did these symptoms first appear, Whether the symptoms are constant or intermittent, Any diagnostic codes from your ECU, If you notice the issues more during cold starts These details would help determine if your boost leak symptoms match what I experienced and whether you might be facing the same actuator valve issue.

Thanks for the responses regarding the turbocharger issues. Just had my latest service at 195524 KM. The symptoms started appearing gradually over the past 3 weeks. My OBD scan shows error code P0299 related to insufficient boost pressure. The whistling noise and power loss are definitely more noticeable during cold starts. The turbo actuator diagnosis makes sense given these symptoms. Going to have the pressure sensor and actuator valve checked first since they seem to be common failure points. Hoping its just the bypass valve like in your case and not a more extensive turbocharger repair. Will update once the workshop determines the exact cause of the boost leak and completes the repair.

Thanks for the update on your Q8's symptoms. The P0299 code and cold start issues strongly align with my Q7's turbo problems from last year. The combination of insufficient boost pressure and that signature whistling noise during cold starts is a classic sign of actuator valve failure. In my case, replacing just the turbo actuator valve wasnt enough, the pressure sensor had also degraded over time, leading to inaccurate boost pressure readings. When both components were replaced together, it completely resolved the boost control issues and restored proper turbocharger function. Since your mileage is close to what mine was when the problem occurred (I was at around 190000 km), and the symptoms are nearly identical, Id strongly suggest having both the actuator valve and pressure sensor checked. The complete fix including both parts ran about 400 Euro in my case, but it was worth avoiding potential damage to the turbocharger wastegate from continued malfunctioning. Keep monitoring for any changes in the symptoms, especially the cold start behavior and whistling noise. These can indicate if the boost pressure control issue is getting worse.

The symptoms you described match exactly what I was experiencing. Based on my current mileage of 195524 KM and the P0299 error code, it seems our issues are very similar. The cold start problems and whistling noise definitely point toward the pressure sensor and turbo actuator being the likely culprits. I appreciate the detailed information about your repair experience. Good to know the complete fix including both the actuator valve and pressure sensor cost around 400 Euro. That helps set realistic expectations for my upcoming workshop visit. The gradual onset of symptoms over 3 weeks matches the typical pattern of failing boost control components. Will definitely have them check both the actuator and pressure sensor since replacing just one might not fully resolve the turbocharger issues. Will book the workshop appointment this week and have them investigate the boost leak thoroughly. It is reassuring to know this is likely fixable without major turbocharger repairs. Will update the thread once I have more information about the actual fault and repair costs.