Seat Ibiza rough running and exhaust smell

Rough running, a strong exhaust smell, and the check engine light suggest an exhaust treatment system issue. The Ibiza's exhaust system isn't too complex, but a defective lambda sensor (or oxygen sensor) could cause this. Is the exhaust leaking near the exhaust pipe or further downstream? Does your car use DEF fluid, and is it at the correct level? Also check the EGR valve, as it can cause similar issues. Does the engine run rough all the time, or only at certain speeds or when cold?

The exhaust seems to be leaking near the middle of the car, but I can't pinpoint the location. I'm not sure about DEF fluid. Where is the EGR valve located, and how can I check it? The engine runs rough most of the time, but it’s worse when cold.

Given the exhaust leak location, the lambda sensor could be corroded or damaged. Combined with the rough running, it's likely the problem. The EGR valve is usually near the intake manifold, but checking it requires tools and know-how. Considering the symptoms and mileage, I'd recommend a workshop diagnosis. It could become a more serious issue if ignored.

The workshop confirmed the lambda sensor was the issue. They replaced it. The check engine light is off, the engine runs smoothly, and the exhaust smell is gone. The total cost was 375€.