Exhaust smoke and some clattering

[E_S]

If I leave my car idling for more than a minute or two, it will start smoking a bit. No visible smoke while driving, I think. In addition, I think the engine is clattering a bit too much when warm - as loud as when cold. It does not use any oil or coolant. I'm thinking maybe the injection timing has changed due to wear and tear and/or that the 190k miles old injectors are getting worn. Any opinions?