Audi A5 TDI Boost Failure Signs & Troubleshooting

Had similar issues on my A4 2.0 TDI from 2014. The symptoms match what I experienced, sluggish acceleration, check engine light, and that distinctive whistling noise under load. The diagnosis revealed a faulty wastegate actuator and a damaged MAP sensor. The wastegate was stuck partially open, causing inconsistent boost pressure and the erratic performance. The boost pressure sensor readings were all over the place. When the mechanic checked, the wastegate rod had excessive play and wasnt responding properly to pressure changes. This is definitely a serious issue that needs immediate attention. Running with a defective wastegate can lead to turbo failure or engine damage over time. The repair involved replacing the complete wastegate assembly and MAP sensor to restore proper boost control. The repair time was about 6 hours due to the turbo location. The turbo itself was fine in my case, but its worth having them check the shaft play and compressor wheel while they have access. Recommend getting it checked soon, these symptoms typically dont improve on their own and can lead to more expensive repairs if left unchecked.

Thanks for the detailed response about the wastegate and MAP sensor issues. This really helps narrow down what I could be dealing with. My symptoms sound nearly identical, especially the turbo lag and whistling. Did you experience any intercooler problems during the repair? Since I noticed the high fuel consumption, Im worried the whole turbocharger system might need inspection. Can you remember roughly how much you paid for the repairs? Just want to have a ballpark figure before heading to the shop. Also, has everything been running smoothly since the fix, or have you noticed any other boost control issues popping up?

Finally got the car back from the mechanic and can give you a proper update. The diagnosis was spot on, it was indeed a bad boost pressure system caused by a defective wastegate valve. Total repair cost came to 860 Euro, which included labor and parts. The MAP sensor and intercooler were thoroughly tested but showed no issues. The turbocharger itself was in good condition, just the wastegate causing all the trouble. The boost control is now working perfectly, with no more whistling or performance problems. Since the repair, fuel consumption has returned to normal and the engine response is crisp again. No check engine lights or other boost-related problems have surfaced in the weeks following the fix. The turbocharger is performing exactly as it should. Worth mentioning the mechanic did a full pressure test on the entire system while it was apart, which confirmed no other leaks or issues. If your symptoms match what I experienced, you're likely looking at a similar repair scope and cost.

Thanks for the input. Just got back from the mechanic with the final verdict. They found the wastegate actuator was failing, exactly as suggested. The throttle body also needed cleaning due to carbon buildup, which was contributing to the stalling issues. Total bill came to 920 Euro for parts and labor. They pressure tested the whole system too, the intercooler and MAP sensor checked out fine. The boost control is now working perfectly and that annoying whistle is gone. The car feels completely different now, quick throttle response, smooth idle, and back to normal fuel consumption. The mechanic showed me the old wastegate parts and the wear was pretty obvious. Glad I didn't wait any longer as it could have damaged the turbo. Great to have reliable advice before going in, helped me avoid getting upsold on unnecessary repairs. Really appreciate all the technical insights shared here.