Idle stepper motor....little black cylindrical thing near the throttle held on with 2 small allen screws.
They tend to get gunged up easily, take it off carefully as there is a fibre gasket underneath and give the internals a good dosing of WD40 or electrical contact cleaner or similar before refitting.
Inside there is a sealed motor and a chamber with a moving blade to control airflow through the idle circuit, this blade is the bit where the muck collects.
It's usually a good idea to disconnect your battery before removing the motor in order to do an ECU reset which tends to help recognise the "new" component you have just fitted when you restart the car.
You can usually get away with cleaning the stepper several times before it becomes intolerably annoying, a new one can cost up to £110 or so from Alfa.......maybe more these days!