Seat Inca Diesel Engine Trouble

A faulty fuel level sensor could cause those symptoms. Engine stalling at idle and the check engine light are classic signs. Does the dashboard show an obviously incorrect fuel level? Have you checked the fuse box? Some cars have a dedicated fuse for the fuel level sensor.

I haven't noticed anything weird with the fuel gauge on the dashboard, it seems to move normally. Where would I find the fuse for the level sensor? Is it usually marked?

The fact that the fuel gauge seems normal doesn't rule out the sensor. The sensor itself might be sending erratic data to the ECU, triggering the stalling and error light, even if the gauge reads okay. The fuse location is usually in the owner's manual. If you don't have it, check the fuse box cover; it often has a diagram. If the fuse is fine, a faulty sensor is the likely culprit. I suggest getting it checked at a workshop.

It was the level sensor. Replacement cost 52€. Thanks for the help!