I have a mercury mystique that vibrates at idle. it idles at about 550 rpm while in drive which seems low to me and when im idling if i rev up the engne the vibrating goes away. i dont know what the problem could be because i have recently gotten a tune up, changed the air filter and have done my regular matenance. The car seems to vibrate worse when it is colder outside. When idling in park it still vibrates just not as bad. It vibrates the most when the car is in reverse. Im just wondering what could most likely be making this vibration.