Chevrolet N400 Stalling Rough Idle

Those symptoms do suggest fuel delivery problems. A defective fuel volume regulator is certainly a possibility, especially with the reduced power. Has the vehicle also been exhibiting any rough idling or engine misfire symptoms, especially when accelerating? Before condemning the high-pressure pump, have you checked the fuel filter and lines for any blockages or restrictions?

Yes, there is definitely some rough idling, especially when the engine is cold. I haven't checked the fuel filter and lines myself - is this something a novice like myself can easily do, or does it require specialized tools and knowledge? Where should I even start looking?

Given your novice status and the potential seriousness of the issue, I would strongly recommend taking your Chevrolet N400 to a trusted and certified workshop. Diagnosing fuel injection problems can be tricky and requires specialized equipment. A professional can accurately pinpoint the source of the problem and ensure a proper repair. It sounds like it may well be the high pressure pump, but diagnosis is key here.

I'll schedule an appointment with a reputable mechanic to diagnose the problem. As suspected, the high pressure pump was indeed defective, and after replacement of the pump and regulator the problem is gone. The repair cost was 1510€. Thank you for your help and guidance!