Advice needed low idle refs

Hi there, please have grace when giving advice because I’m a woman and don’t know much. My 2005 Nissan Almera is giving me issues. I thought it was maybe the spark plugs. When I’m standing still, idling. The car idles at 500 refs and not the usual 750+.

When the car is warm, and I slow down at a crossing or a stop, it drops in idle refs and almost feel like the car wants to die. It idles almost like it wants to misfire. I even feel the vibration under my seat (bum).

I don’t know, it’s hard to explain. What can it be?