Here's what happening with mine. I can be sitting there idling, and the car will rev by itself up to 1.5 or 2 thousand rpms, and then drop down to below 1 and kind of shudder, almost like when you stall. It's not as harsh as that, but I still notice.

 

Hasho1988, when my problems happened, the transmission light on the dash was flashing so i pressed the check button, and it said that i had low engine oil pressure and also low coolant, so it sounds like you are having the same problem as i am. As about what to do about it and what the diagonistic is, i can't tell you right now but i am hoping to get my car back from the stealership tmrw afternoon/evening at which point i will talk to them and see what they said and then relay the information your way.

BrianVarick, i dunno about your problem. It is slightly different than mine as you can see but i don't know what could be causing it. sorry

 

I had the same problem with mine for a while actually, when I took it in to my mechanic they said it was the coils, oil was leaking into the coils cause I had a bad gasket so every couple of months a new coil would fail, so I switched out the gasket and all the coils and now it runs like new, except for the fact that my check engine light is on, I have to get that checked also I just don't have the funds right now.

 

Oil won't make the car shudder, only effect from switching like that would be loss in power. Shuddering in general could be a problem with the ignition system; plugs, coil packs, etc.. But the weird idle would point towards something else. I would check what has been said already, vacuum lines,fuel pump, o2 sensors. Maybe check the cat, if that is bad it will smell like eggs. A bad/clogged cat could be choking the engine.