Vectra poor starting high fuel consumption

Sounds like a throttle problem. Have you tried cleaning the throttle body? Sometimes gunk buildup messes things up. Does the engine idle rough too?

I haven't cleaned the throttle body yet. The idle is a bit erratic. If cleaning doesn't fix it, could the control valve be failing and need the throttle valve assembly replaced, or should I replace the accelerator pedal module?

Cleaning is worth a shot, it's easy and cheap. But if it's still acting up, the control valve or the whole throttle body could be shot. Get it checked by a workshop before replacing parts. They can diagnose it properly.

I consulted a workshop, and they said it was a defective accelerator pedal module, like we thought. Replacement cost 205€, and it fixed the starting issues and fuel consumption. Thanks for the help!