I too have been chasing this problem as i thought it to be coilpack related. I've changed plugs (ngk iriways), splitfires, taken off the afm, throttle body and ISC valve and cleaned them to no avail. The only thing left for me to do is get the injectors cleaned ultrasonically, change the fuel filter, double check my timing at idle, and change the 02 sensor, which i'm hoping is the culprit - i've been told the 02 sensor controls rpm at idle, not the afm.....