2006 A4 vibrates when in gear under load
 

Kinda a newbie here I have been here just looking at old posts for a couple of years but now I have hit a road block. 2006 A4 cabriolet has 139K miles changed the timing belt plugs and coil packs, Cleaned the MAF, Changed O2 sensors car runs great until you put it in gear and its under a load then it vibrates, Im thinking that it might be the snub mount. My son thinks that its stuck in limp mode ( he is a very good Mech. ) although we just cant figure out why we are getting this vibration. Are we missing something obvious ?