Fuel injected engines use a seperate idle "circuit" for the air intake with a computer controlled idle positioner. The main throttle body is closed at idle.
With time the idle circuit becomes clogged with carbon and needs to cleaned periodically.
Remove the throttle body and clean it with carburetor cleaner and a tooth brush or whatever. Your local auto "zombie" will have carb. cleaner.
Don't get any carb. cleaner on your paint.