Q7 Power Loss & Smoke Points to EGR Valve Issue

I had a very similar issue with my 2018 Q7. As someone with moderate car repair experience, I can relate to your symptoms, especially the power loss and rough idle. Initially, I suspected a vacuum leak due to the hissing sound, but after proper diagnostics, it turned out to be a faulty EGR valve affecting the exhaust gas recirculation system. The black smoke was a clear indicator of improper fuel-air mixture. My workshop ran a full diagnostic check and confirmed the EGR valve was stuck partially open. They cleaned the valve first to rule out carbon buildup, but ultimately it needed replacement. The total repair cost was 355 Euro, including parts and labor. Since the fix, fuel economy improved significantly and the check engine light hasn't returned. Before jumping to conclusions, could you share: Current mileage? Service history? especially regarding EGR system maintenance? Any recent changes in fuel type or brand? Does the problem get worse when the engine is hot or cold? This information would help determine if your issue matches what I experienced with my Q7. Also, while waiting for repairs, I would avoid heavy acceleration to prevent potential catalytic converter damage.

Thanks for the detailed input. My Q7 has 104617 KM and just had its annual service last month. The symptoms get significantly worse when the engine reaches operating temperature. Since the last service, I have not changed fuel type or brand. The rough idle becomes very noticeable after about 10 minutes of driving. I did have the check engine codes read yesterday. They point to improper exhaust gas recirculation values, but the mechanic mentioned testing the entire system before replacing parts. What concerns me is the combination of symptoms, especially the black smoke and power loss. The vehicle emissions seem clearly affected. What diagnostic tests did your workshop perform to confirm it was specifically the EGR valve and not another component in the system?

Based on your mileage and symptoms description, your situation sounds nearly identical to what I experienced. When my Q7 reached around 100000 KM, the symptoms also worsened with engine temperature, which is a classic sign of EGR valve issues. My workshop performed several specific tests: 1. They monitored the live data stream from the EGR valve position sensor while varying engine load 2. Performed a smoke test to rule out any vacuum leak in the intake system 3. Checked the EGR cooler for blockage 4. Tested EGR valve operation in both cold and hot conditions The black smoke in your case, combined with the power loss and confirmed recirculation value errors, strongly suggests an EGR valve malfunction rather than a peripheral component. The fact that symptoms worsen at operating temperature matches my experience exactly. Quick tip from my repair: have them check the EGR cooler while they are working on the system. In my case, it was partially clogged with carbon deposits, which contributed to the poor vehicle emissions. Getting both cleaned at once saved me money in the long run. For reference, after my repair: fuel consumption returned to normal within 2 tanks, check engine light cleared permanently, black smoke disappeared completely, power response became smooth again, emissions test passed easily. Since your symptoms match mine so closely, I would recommend authorizing the complete EGR system inspection they suggested.

Thank you for sharing those specific testing details. This definitely helps narrow down my issue. Given the matching symptoms and similar timing of failure, I am more confident now about proceeding with the EGR system inspection. The progression pattern you described, especially how the symptoms worsen at operating temperature, matches my situation perfectly. I am particularly concerned about passing my upcoming emissions test, so addressing this promptly seems wise. I will request they check the EGR cooler during inspection, as the carbon deposit issue you mentioned could explain the severity of my symptoms. Their suggested diagnostic approach aligns with the thorough testing sequence your workshop performed. One last question, did you drive the vehicle much between initial diagnosis and repair? I am wondering if I should limit driving to prevent potential catalytic converter damage while waiting for the repair appointment next week.