Seat Ibiza engine issue

Sounds familiar. Had a similar issue with my old Renault Megane. Check engine light, power loss, the whole shebang. Was it throwing any codes related to temperature fluctuation?

Temperature fluctuation, you say? How did you diagnose that specifically? Was it just trial and error?

The code reader pointed to emission control issues and the temperature sensor itself. Once the sensor was replaced, the mechanic found a small crack in the exhaust manifold near the sensor. You might want to get it checked at a workshop.

Thanks for the insight. It was indeed the exhaust temperature sensor. Replaced it, and the exhaust leak was sealed. Cost me 265€, but the car is running smoothly now.