vibration while idling

My JDM 2000 Galant (2 litre VRG GDI) vibrates quite a lot when idling with the gear in "D" or "R" and the foot brakes on. (This is irritating while waiting for the traffic lights to change.) If I lift my foot from the brake (but with the handbrake pulled to prevent the car from moving), the vibration goes away. If the gear is in "P" or "N", there is no vibration, even with my foot on the brake.
Somehow the foot brake lowers the RPM when the car is stationary in "D" or "N" and thus leading to the vibration. Mitsubishi's service guy tuned the engine / ECU twice but to no avail. Would appreciate if anyone can enlighten.

Maybe the brake servo is faulty
Just guess to be honest

If it only happens when you have your foot on the brakes, it could be your alternator is getting weak. Does it get worse at night with the headlights on? If it doesn't, forget what I said.

Thanks for helping to trouble-shoot. The vibration is there regardless of headlamps or air-condition are switched on or not. Someone was telling me it could be Air control valve OR crankshaft pulley / damper.

I have to admit i don't know exactly where is the air control valve or which pulley / roller is the crankshaft puley / damper. So if any of you guys can help illustrate exactly where these are under the hood via websites or picts, it would be greatly apreciated. Thanks.

Sorry...can't help you there, you have a JDM spec

look at your engine bay. i believe its on the passenger side. look to the side of the motor. there will be belts there. black rubber belts right? well those belts turn the pulleys for the AC power steering, alternator etc...