Thalia rough idle error code

That sounds familiar! I had a similar issue with my old Opel Astra. The engine was vibrating like crazy, and it turned out to be a failed mount. The error code was a big clue. Have you checked the mount itself for any visible damage? It might be something obvious, like a crack or separation.

Thanks for the tip! I visually inspected the mount, but didn't spot any cracks. Is there a way to test the mount more thoroughly? Like, is there a way to make sure it's really the mount before I replace it?

Well, short of having a professional look at it, it's tough to be 100% certain without specialized tools. The error code and the uneven idling are strong indicators though. Given that you've checked the connections, it's pointing towards the mount itself being defective. I'd suggest taking it to a workshop. In my case, I postponed it for too long and the vibrations caused damage to other parts.

Thanks a lot for your help! I took it to the workshop, and you were spot on. Turns out it was indeed a defective engine mount, just like you suspected. They replaced it for 95€, and the car runs smoothly again.