It's already been mentioned several times that it is mainly in the tuning, which I also experienced in my own car. I had GSC S2 cams installed and initially the idle was extremely lopey, and once it was retuned, it definately smoothed the idle back out.

 

At even 14 degrees with idle sensitivity timing limit set to 5 and 14.7 +/1 0.2 AFR (closed loop) and 1000rpm it lopes quickly then stumbles out a rough idle then back to loping. That's as smooth as I can get it at this stage.

 

VIdEO