SQ5 TDI Rough Running: Intake Manifold Warning Signs

Had a very similar issue with my Q7 3.0 TDI (2016). As someone with moderate experience working on VAG diesels, I can share my troubleshooting journey. The symptoms matched yours exactly, rough idle, engine misfire, and performance issues. After monitoring the manifold pressure sensor readings, it became clear the intake system wasnt holding proper pressure. The workshop confirmed a gasket leak caused by heat damage to the intake manifold. The complete diagnostic process included: Pressure testing of the intake system, Manifold sensor data logging, Visual inspection for carbon deposits, Air intake flow measurement The workshop had to replace the entire intake manifold assembly since the scorching had warped the mounting surfaces. Total repair cost was 1180 Euro including parts and labor. The difference in performance after repair was remarkable, smooth idle returned and power delivery became consistent again. Before offering more specific advice, could you share: Current mileage on your vehicle? Any recent maintenance history? Are you getting specific error codes? Have you noticed any changes in fuel consumption? This would help determine if your issue matches what I experienced and whether you might need similar repairs.

After checking my maintenance records, I last serviced the car at 95000KM, about 2000KM ago. The workshop already performed a basic vacuum leak test but found nothing conclusive. The engine misfire symptoms persist, especially during cold starts. A with diagnostic equipment detected error codes related to intake manifold pressure deviations, suggesting possible gasket leaks in the system. The air intake readings seem inconsistent according to the scan tool. Before committing to a full manifold replacement, I want to ensure all diagnostics point to this being the root cause. My current mileage is 97118KM and these issues started about 3 weeks ago without any prior warning signs. The fuel consumption has increased noticeably, adding to my suspicion of an intake-related problem. Would you recommend any specific tests beyond what has been done to definitively confirm if the intake manifold needs replacement?

Thanks for the additional details. Your symptoms and diagnostics align even more closely with what I experienced. The sudden onset and error codes pointing to manifold pressure deviations, combined with increased fuel consumption, strongly suggest intake system issues. In my case, before replacing the manifold, we performed smoke testing which revealed hairline cracks not visible during basic vacuum testing. The inconsistent air intake readings you mentioned match my experience, they were a key indicator of manifold problems rather than just gasket leaks. Given your mileage is similar to when my issues occurred (I was at 98000KM), and considering the common failure points of these engines, I would recommend: Smoke testing the entire intake system under pressure, Checking the manifold sensor readings at different RPM ranges, Inspecting for carbon buildup around manifold sealing surfaces, Testing actuator functionality on the intake flaps The basic vacuum test might miss smaller leaks that only manifest under specific operating conditions. My initial tests also seemed inconclusive until more thorough diagnostics were performed. The repair cost me 1180 Euro, but catching it early prevented additional engine damage. The workshop found the manifold had developing stress cracks, a common issue at this mileage point. After replacement, both fuel economy and performance returned to normal.

Based on all this valuable feedback, I think I need to proceed with more comprehensive testing. The similarities in symptoms and mileage are too close to ignore, especially with the manifold sensor readings showing irregularities. My engine performance issues match exactly what you experienced, from the cold start problems to the fuel consumption increase. The check engine light and manifold pressure deviations definitely point toward intake system problems. Since the basic vacuum test wasnt conclusive, I will arrange for smoke testing and detailed manifold sensor diagnostics as suggested. The 1180 Euro repair cost seems reasonable considering the potential for further engine damage if left unchecked. I will contact a workshop that can perform these specific tests, particularly the smoke testing and intake flap actuation checks. Given how the symptoms developed suddenly at around 97000KM, similar to your case, I suspect a full intake manifold replacement might be necessary. Will update once I have the complete diagnostic results, but your experience has helped narrow down the likely cause and required repair approach.