A stumble is not what I feel. It is just sometimes a rough idle where I can feel a very very slight vibration in the car when it happens. nothing as drastic as a stumble feeling like you metnioned. Also, my engine idles around 700 to 800 rpm mostly. When the vibration hits.. I can see the tach go from 800-700 and then to 800 again.. ever so slightly.

I am comparing this to my Acura TL that I have which has a super smooth engine that you would not know it on when you are at a stop light and the tach is always dead stuck at 800 during idle...

Another reasoning for this slightly rough idle could be due to the fact that the Crossfire engine is a 3 valve design with a single OHC (I don't know if it has a blance shaft to smooth the engine or not). All of my toyota and acuras have been DOHC designs which are by design more balanced than a single over head cam design.. which could explain the slight vibration in the engine...