Weird vibration with A/C on while stopped

:( Alright. First, it is a 2000 hyundai accent, 26000 miles. Clean air filter, changed fuel filter last september, cleaned fuel system last week, changed spark plugs, oil changes up to date, changed transmission oil. I live in a tropical climate.

The problem is that after turning on m car, after 2-3 minutes, if I place it on drive, 1 or 2 while stopped my car vibrates. Only does it when it is stopped, it goes away when I drive and comes back when I stop. It gets worse with the air coditioner on. My mechanic adjusted the rpm to 900 and it didnt change a bit. It is almsot not felt I neutral.