Ford Ka check engine light air intake issue

Could be a defective hose connection from the air pump to the valve. Have you checked the vacuum hoses for any cracks or leaks? A vacuum leak can cause all sorts of problems with the air supply and trigger that engine light. It may even make the engine stall.

Thanks! That's really helpful. By vacuum hoses, do you mean the small, rubbery ones connected to the intake manifold? Is there a specific test I can do to check for a vacuum leak besides visually inspecting them?

Yes, those small rubbery ones. A visual inspection is a good start, but tiny cracks can be hard to spot. You could try spraying some carb cleaner or starting fluid (very carefully!) around the hoses while the engine is running. If the engine revs up slightly, that indicates a leak in that area. But honestly, for a guaranteed diagnosis, a garage will be the best bet.

Thanks a lot for the advice! I took it to a workshop as you suggested, and it turned out to be a defective hose connection from the air pump to the valve, just like you said. Repair cost me 175€, but the check engine light is now off!