Stagea rough running and misfires

Rough running, check engine light, jerking, and reduced power definitely point towards combustion issues. Given the symptoms, a defective injection valve/injector is a likely cause. However, before jumping to conclusions, have you checked the ignition coils? A failing coil can also cause misfires. Misfires mean that the fuel/air mix isn't burning correctly in one or more of your cylinders. Does the 'jerking' feel like a sudden loss of throttle response? Does it mostly happen at a specific RPM range?

Thanks for the quick reply! I haven't checked the ignition coils yet, I'll add that to my list. The jerking is most noticeable when I'm trying to accelerate quickly, like when merging onto the highway. It does feel like a sudden loss of throttle response. Is there a way to test the injection valve/injector myself, or is that best left to a professional?

That acceleration-related jerking strengthens the misfire theory significantly. While you could technically test the injectors yourself using a multimeter to check their resistance (search for Nissan Stagea injector resistance test), interpreting the results accurately and safely diagnosing a specific faulty injector requires some experience. Given the symptoms and the potential complexity, it's probably best to take it to a workshop. They have the tools to properly diagnose which injector is failing, or even if that is definitely the issue. You might save time and money in the long run.

Thanks, I appreciate the advice. I took it to a shop, and they confirmed it was a defective fuel injector and replaced it. They also cleared the error codes. The total cost was 515€. The Stagea is running smoothly again!