Touareg V6 Power Loss Points to Boost Control Issue

Had almost the exact same issue with my 2019 Touareg V6. Started with power loss during acceleration and poor fuel consumption. After some diagnosis, it turned out to be a vacuum leak caused by a defective vacuum switching valve. The symptoms match what you describe, especially the sluggish acceleration and boost pressure faults. The vacuum leak was affecting the intake manifold pressure, creating issues similar to turbo lag during acceleration. The repair involved replacing the faulty bypass valve and checking all vacuum lines. Total cost was 140€ including parts and labor. After the fix, power delivery returned to normal and fuel economy improved significantly. Before suggesting specific solutions, could you share: Current mileage on your Touareg, whether you notice any unusual sounds during acceleration, if the issue gets worse when the engine is warm, what specific error code your scanner shows. This information would help determine if your issue is similar to what I experienced. A proper vacuum system test would likely identify the exact problem point.

Had the last service at 91000km and they found no issues back then. Since your symptoms match mine completely, I also notice a slight whistling sound during acceleration. The error code from my scanner is P0299. The problem definitely gets worse when the engine is fully warmed up, especially on hot days. On cold mornings it runs much better. The boost solenoid idea makes sense given how engine performance drops specifically under load. My intake manifold also shows signs of carbon buildup which might be contributing to the pressure drop issues. Will have the shop check the vacuum lines and bypass valve as suggested.

Yes, those additional details strongly point to a vacuum system issue, just like what I dealt with on my Touareg. The P0299 code (turbocharger underboost condition) combined with the whistling sound and temperature-dependent symptoms perfectly matches my experience with the faulty vacuum switching valve. The carbon buildup you mentioned can definitely compound the engine performance problems. In my case, after fixing the vacuum leak, I also had the intake manifold cleaned which helped restore optimal pressure sensor readings and boost control. Quick tip from my repair: have them pressure test the entire vacuum system, not just the bypass valve. My mechanic found that the heat had also damaged some nearby vacuum lines, making the engine performance issues worse. Replacing those cracked lines along with the valve made a significant difference in boost control and fuel economy. For reference, the complete fix on my Touareg included: New vacuum switching valve, Replacement of 2 vacuum lines, Intake manifold cleaning, System pressure test Total cost came to around 280€, but it completely resolved the turbo lag symptoms and restored proper engine performance. The whistling sound you described disappeared immediately after the repair.

Thanks for sharing those details about your repair experience. The whistling noise during acceleration combined with P0299 does sound exactly like what you encountered. Really helpful to know the pressure sensor wasnt the culprit in your case. Based on my symptoms and mileage (91000km), I will definitely have them inspect the vacuum system thoroughly, focusing on the boost control components and vacuum lines. The fact that engine performance improves on cold starts but degrades with heat matches the vacuum leak theory perfectly. Since my intake manifold already shows carbon buildup, I might as well get that cleaned while they check the vacuum switching valve and lines. The total repair cost of 280€ seems reasonable to restore proper boost pressure and fix the acceleration lag. Will schedule an appointment to have them run the full system pressure test. Hoping a similarly straightforward vacuum system repair will resolve my engine performance issues too. Thanks for walking through your experience, gives me a much clearer picture of what to expect at the shop.