Audi A5 TDI Turbo Problems Causing Power Loss

I had a very similar issue with my A4 2.0 TDI from 2015. Based on some experience with diesel engines, I can share what worked in my case. The symptoms you describe match exactly what I experienced, poor performance, increased fuel consumption, and that annoying turbo lag. After checking with my workshop, they found a faulty vacuum switching valve affecting the boost controller system. The pressure sensor readings were all over the place, causing the boost solenoid to malfunction. The fix involved replacing the vacuum switching valve, which resolved the pressure drop issues and restored proper boost control. Total cost was 140 Euro including parts and labor. Before jumping to conclusions though, we should verify a few things about your specific case: 1. Have you noticed any unusual sounds when the turbo spools up? 2. Does the engine show any signs of compressor surge under heavy acceleration? 3. What error codes is the check engine light showing? 4. Has there been any recent maintenance work done? Could you share these details? It would help determine if your issue is identical to what I experienced or if there might be other factors at play. Also, while my repair was straightforward, its best to get a proper diagnostic scan to confirm the exact cause in your case.

Latest service was done at 88000KM, just 2 weeks ago. I can hear a distinct whistling noise during acceleration, which makes me suspect a vacuum leak somewhere in the intake manifold system. No compressor surge noticeable, but the boost pressure seems inconsistent. Error code reader shows P0299, underboost condition. The boost controller and bypass valve were visually inspected during my recent service, but no issues were noted then. However, the symptoms have become much more pronounced in the last few days, especially after highway driving. The pressure sensor readings fluctuate significantly according to the diagnostic computer. This started happening right after the symptoms became more noticeable. Has anyone checked if this could be related to the intercooler system? The temperatures here have been quite variable lately.

Thanks for providing those additional details. Your situation sounds even more similar to what I experienced, especially with that P0299 code and the whistling noise. In my case, while the initial visual inspection also showed no obvious issues with the bypass valve, the fluctuating pressure sensor readings turned out to be a key symptom. The intake manifold pressure was dropping unexpectedly, causing the turbo lag and performance issues you described. The intercooler system was actually part of my problem. The connection between the intercooler and intake manifold had developed a small leak, leading to inconsistent boost pressure. This explained the whistling noise and pressure drop I was experiencing. The pressure sensor readings were erratic because of this leak, not because of a faulty sensor. The repair involved: Pressure testing the entire intake system, Replacing the intercooler hose connections, Recalibrating the boost pressure control system Total repair cost came to 280 Euro, more than just a vacuum valve replacement, but it completely resolved the issues. The turbo lag disappeared, and fuel consumption returned to normal. Given your identical symptoms and that P0299 code, I would strongly suggest having the intercooler connections checked, particularly since the issues worsened after highway driving where the system is under more stress.

Based on the details you provided, I'm having my mechanic check the intercooler connections first thing tomorrow. The P0299 code and similar symptoms definitely point toward a boost pressure control issue. Its reassuring to hear your turbo lag and performance problems were fully resolved after fixing the intercooler system and recalibrating the boost controller. The whistling noise during acceleration matches what you described, and since my issues also worsened after highway driving, the intercooler connection leak seems like the most likely cause. The fluctuating pressure sensor readings and inconsistent boost pressure fit this diagnosis perfectly. I appreciate the detailed breakdown of the repair process and costs. 280 Euro seems reasonable for a complete fix, especially if it includes pressure testing and recalibration of the boost solenoid system. At least now I can go to my mechanic with a clear idea of what to check first, particularly the connection points between the intercooler and intake manifold. Will report back once the inspection is done. Hopefully, its just the intercooler connections and not a more serious issue with the bypass valve or turbo system itself.