Q2 Turbo Issues: Low Power and High Fuel Usage

Had similar symptoms on my Q3 2018 TFSI. The main issue turned out to be a faulty vacuum switching valve causing compressor surge and irregular boost control. Diagnosed after noticing inconsistent engine performance and excessive turbo lag. The repair required accessing the intake manifold to replace the vacuum switching valve and checking the boost solenoid connections. The workshop found slight wear on the surrounding vacuum lines which were also replaced to prevent future leaks. This is a known weak point that can cause significant performance issues if left unchecked. The repair is straightforward but requires proper diagnostic equipment to confirm the vacuum leak and test the new components. A complete fix restored normal boost response and resolved the high fuel consumption. Worth getting checked soon as continued driving with a vacuum leak can potentially lead to more serious engine performance issues. The engine warning light in these cases typically indicates the ECU detecting irregular boost pressure readings.

Thanks for sharing that experience, matches my symptoms exactly! Really helpful to know about the vacuum switching valve being the culprit. My engine performance has been all over the place just like you described. Did you remember roughly what the total repair cost was? Also curious if youve had any other boost-related issues since getting it fixed? My pressure sensor readings have been inconsistent according to the OBD scanner, so wondering if I should have them check that too while theyre in there.

The repair bill came to 140 Euro for replacing the defective vacuum switching valve. Since the fix, the boost controller has been working flawlessly with no pressure drop issues. The bypass valve and all pressure sensor readings are now consistently normal. The mechanic did a thorough check of the entire boost system while doing the repair. They confirmed the pressure sensor was actually working fine, the inconsistent readings were just a symptom of the faulty vacuum valve. Once that was sorted, all sensor readings returned to normal. Its been about 8 months since the repair and the turbo lag issues havent returned. Fuel consumption is back to normal and the engine performs exactly as it should. Getting it fixed promptly definitely prevented any additional wear on the system.

Thanks for the input. Finally got it sorted yesterday at a new shop. They diagnosed the exact same vacuum switching valve issue causing the turbo lag. The mechanic showed me where the intake manifold pressure was fluctuating due to the failing valve. Total bill came to 165 Euro including labor and a full inspection of the boost system. They also noticed and replaced a cracked vacuum line near the bypass valve that could have caused problems later. The compressor surge is completely gone now and the car pulls strong again with no hesitation. Really glad I asked here first, saved me from getting unnecessary parts replaced. The engine light cleared right after the repair and fuel economy is already much better after just one day of driving. Going to keep an eye on the boost readings for a while just to be sure everything stays stable.