Kubistar Injection Fault

Sounds like a pain. When an injection system acts up with those symptoms, I'd suspect a leak or a bad connection. Have you checked the cable or plug connections to the injectors? A loose or corroded connection can cause all sorts of weird issues with fueling and performance. By the way, does the 'check engine' light come on?

Yeah, the check engine light is on, forgot to mention that. I visually inspected the connectors but didn't see anything obvious. Is there a way to test them more thoroughly without specialized tools?

Without special tools, it's tough to be 100% certain. Given the symptoms and the check engine light, a defective cable or plug connection is very likely. You could try wiggling the connectors while the engine is running and see if the idle changes, but be careful! Really, at this point, a workshop visit is probably the most efficient way forward.

Thanks for the advice. I took it to a workshop, and you were spot on – it was a defective plug connection on one of the injectors. They cleaned it up and secured it properly. Cost me 95€, but now it runs like new again!