A4 TDI Intake Manifold Issues: Hissing & Performance Drop

The symptoms you describe sound very familiar. Had a similar issue with my 2012 A5 2.0 TDI about a year ago. As someone with moderate experience working on diesel engines, these intake manifold problems are quite common on these models. Started exactly the same way, engine misfire symptoms, poor performance, and that characteristic hissing sound from the intake system. The engine management light stayed on constantly, and the car felt notably underpowered. The flap control unit in the intake manifold was indeed the culprit. Initially considered replacing the entire intake system, but the workshop confirmed only the control unit needed replacement. The repair cost me 465 Euro including parts and labor. Since the fix, the car has run perfectly with no recurring issues. For a more accurate diagnosis of your specific case, could you share: Have you done a diagnostic scan for error codes? When was your last intake system service? Does the hissing sound change with engine RPM? Any recent changes in weather conditions when the problem started? The airflow control issues in these engines can sometimes be related to other components, so these details would help narrow down the exact cause.

Thanks for your follow up. My last scheduled service was done just 3 months ago at 51000 KM. I ran a diagnostic scan which showed error code P2015 indicating intake manifold runner position sensor malfunction. The hissing sound definitely gets louder with higher RPMs. No noticeable correlation with weather changes. The engine performance has gotten worse over the past few days. The engine misfire is now more pronounced especially during cold starts. Air intake seems seriously compromised as the engine struggles to maintain steady power. What concerns me is whether this could cause additional damage if not fixed quickly. Some forum posts suggest intake manifold issues can affect other engine components if left unaddressed.

Based on the error code P2015 and worsening symptoms, you definitely need to address this soon. When I had the same issue on my A5, I noticed similar progression, the engine misfire became more pronounced and the intake system problems led to increasingly unstable performance. The flap control malfunction can indeed cause additional issues if left unfixed. In my case, the faulty manifold flap was causing improper air-fuel mixture, which put extra stress on the engine and likely would have damaged other components if left unrepaired. Here is what I learned from my experience: The intake manifold flap tends to fail gradually, explaining your worsening symptoms, Cold start problems are a classic sign of compromised airflow control, Continued operation risks damage to fuel injectors and EGR system, The error code P2015 specifically points to the manifold flap position sensor, matching my diagnosis Strongly recommend getting it fixed within the next week. The repair is straightforward, in my case it took about 2 hours at the workshop. Running the engine with compromised intake system performance will only lead to more expensive repairs later. The good news is that with only 51000 KM, your other components should be in good condition, making this likely an isolated issue with the flap control unit itself.

Thanks for your detailed response and sharing your experience. This all makes a lot of sense now. After reading about your similar case and given how my engine performance continues to deteriorate, I realize I need to get this fixed asap. Your points about potential damage to other components from running with a compromised intake system have me concerned. The matching symptoms, especially the progressive engine misfire and that distinct intake manifold hissing that increases with RPM, really confirm what I suspected. The diagnostic code P2015 seems to definitively point to the flap control issue. Good to hear replacing just the control unit resolved your problem. The quoted repair cost of 465 Euro seems reasonable considering the potential for much costlier damage if left unfixed. Given my relatively low mileage, I hope my repair will be similarly straightforward. I will schedule the repair this week before the faulty intake system causes any additional engine performance issues. Better to address the flap control problem now than risk more extensive damage.