Did you check if the throttle valve closes completely in idle? If you have a scanner with live data, you can see the TPS output, which should be around 12% in idle.
There could be a problem with the IAC stepper motor. Did you check for any fault code(s) set?
JEEP Grand Cherokee 4.7 Lmtd 2004
HID 8000K in low and fog / Quad Squad member
KYB Gas-a-Just shocks / Pirelli Scorpion ATR 245/65/17 - Transgo reprogramming shiftkit.