Corsa rough running poor fuel economy

Sounds frustrating! Reduced power, rough running, increased fuel consumption, and jerking are definitely concerning. Since the air filter is new, we can probably rule that out. Have you noticed any black smoke coming from the exhaust? A rich mixture could cause that. When was the last time you checked your fuel injectors? They could be leaking or not atomizing the fuel properly. What's your air-fuel ratio?

Black smoke? I haven't noticed any, to be honest. As for the fuel injectors, I've never checked them myself. How would I even go about doing that? And how can I check the air-fuel ratio?

Okay, no black smoke is good. As for checking the injectors and air-fuel ratio without proper tools...well, it's tricky. You'd ideally need diagnostic equipment. Given all the symptoms – the rough running, poor fuel economy, and jerking – and the fact that you haven't checked the injectors, it really does sound like they could be the culprit. It might be best to take it to a workshop. It'll cost about 515€ to replace the defective injector.

Thanks for the advice! I took it to a local mechanic, and it turned out to be a defective fuel injector, just as you suspected. Cost me 515€ to get it sorted, but it's running like a dream now!