changing the cabin filter whenev i feel the air flow has reduced too much and running a/c for 15 minutes a week regardless of weather and my 13 year old 2.0d saloon had it a/c serviced only once in 2007 in its life, and still retains 60% gas that came with it.
and that metallic part is called throttle body (thaartal baadi in desi) and the problem is somewhere else(plugs, plug wires, coil, some sensor or ecu), throttle body doesn't get gunky enough to effect proper operation for at least 30k k.