My 07 IS350 runs great, but when it's idling at a stop light, the front-end of the vehicle shivers in D mode and my wife in the passenger seat can feel it, too. If I put it in 'N' or 'P' mode, shivering seems disappears. It idles at around 650-700 RPM.

I've done searches here but can't seem to find answers as to what may cause the shivering.. What would be possible causes of rough idle / shivering at idle?

 

Does the car RPM fluctuating or stay stable at idle? You might have worn-out transmission and/or engine mounts if the problem goes away by shifting to Neutral.

 

Thanks for the reply. RPM is pretty stable during idling.

Is it common for tranny or engine mounts going bad on 2nd Gen IS vehicles? I do know it's very common with Honda/Acura FWD vehicles..

 

^I was going to mention engine/trans mounts as well.

As our vehicles get older, the likelihood of those needing replacement mounts will become more and more.

 

I forgot to mention that when I shift from N to D and vice versa, I can feel the car's movement even with a foot on the brake.

 

Is there a way to test if tranny or engine mounts are bad?

 

From what you described, i think your engine mounts are starting to wear out (as opposed to Tranny mount since the vibration isn't there when you are driving). It is a bit hard to test when they are slightly worn out but the classic symptom is increasing vibration at idle in "D". You could try to look for visible sign of wear/damage. I think our 2IS have 3 set of mounts?
Fortunately, the parts isn't expensive and somewhat easy DIY.

 

From my reading, our mounts are semi-fluid filled; so perhaps they've leaked out or just deteriorated to the point of needing replacing. Yes, they're relatively cheap and easy to replace with a garage, a floor jack, jack stands, a block of wood (to hold the engine up during mount removal/install), and basic hand tools.