The motor mounts did not effect the idle,what happens is that as your mounts fail,They no longer hold the power plant firmly in there grasp,this allows the engine to move around more than when the mounts are new,thus a shake sets in.Kind of like holding a glass of water in your hand and then resting it on the counter less ripples. The smoke test is used by people who like I do not wish to spray flammables on hot engines,the use of smoke is just another way to pin point vacuum leeks. Vacuum sucks,by its very nature,so smoke will follow the leek.I use an old bee keepers smoker and a length of tubing to put the smoke in an area I desire,try it,it is so basic science.JNT