Nissan Multi Uneven Idling

Uneven idling and a stored error code could point to a few things, but a defective motor mount isn't out of the question, especially on a car of that age and mileage (180993 km is getting up there!). The rubber in those mounts degrades over time. However, before jumping to conclusions, it's worth investigating the transmission mount as well, and checking for any obvious vibration issues. What error code is it? Is the vibration constant, or only at certain RPMs? Knowing this helps narrow down if it's truly the motor mount, or something else causing the engine to run rough and trigger a code.

I don’t have the exact error code right now, but the vibration seems more pronounced when the engine is under load, like when I'm accelerating. It feels worse at lower speeds. I am not sure how to investigate the transmission mount. What exactly should I look for?

The fact that the vibration is worse under load and at lower RPMs does strengthen the case for a defective engine mount, or possibly the transmission mount as well. Since you're not comfortable diagnosing it yourself, my recommendation would be to take it to a trusted mechanic. They can properly inspect the engine mounts and transmission mount for wear and tear, cracks, or separation and read that error code, which is crucial. A bad cable or plug connection is also possible, but less likely to cause a strong vibration, and more likely to cause intermittent issues. From the error code, a mechanic will be able to tell the exact issue. For replacement, budget around 95€ for a new mount, but get a quote first!

I took the Nissan to my local mechanic, and it was indeed a defective engine mount as you suspected. They confirmed the cable/plug suggestion. They replaced the faulty mount, and the uneven idling and vibration are now completely gone. The total repair cost was indeed around 95€. Thanks for your assistance!