Hey guys I have a 2011 tC manual with 130kmiles and for a couple weeks now once I put the car in natural it could be at a red light or cruising in neutral downhill, but all of a sudden the rpms will drop to about 500rpm the car would shake and the rpms will go back up to the normal RPM ( ac off ) now with the ac on the car will bounce from 500 to 950 back and fourth like 5 times until it settles again. I've had this car for years and it just started doing this. The car drives normal just until I shift to natural. Now I find a way to prevent the idle issue, if I coast in gear to a stop the car idle will stay steady then shift to natural but if I quickly go from gear to neutral the idle drops then settles ( ac off ) but ac on it bounces like 5 times. I've cleaned my throttle body and it makes a buzz noise when the car is on so idk any advice would help.