Insignia high fuel consumption

A throttle valve issue could be the problem, given those symptoms. Have you thought about a defective accelerator pedal module? That could mess up the throttle position readings and cause similar issues.

Thanks for the suggestion. Is there an easy way to test the accelerator pedal module or throttle position sensor before I replace anything?

Testing varies, but a diagnostic scan is the first step. Faulty readings from the accelerator pedal module point to a problem. Given the potential complexity, I'd suggest a workshop visit for diagnosis and repair. It will save time and potential headaches.

I took it to a shop, and they confirmed the accelerator pedal module was faulty. The repair was 205€, including parts and labor. Thanks for the help.