2002 GMC Yukon Low Idle

Engine starts fine but runs at a very low idle...around 400-500 and surges. With the AC on it does not seem to have enough power to provide cooling....AC works fine at higher speed. When turning at low speed sometimes the steering becomes difficult and engine will die. Have replaced plugs and plug wires but still has the same problem. Have read your section on the IAC, but would like help in checking this on my specific model. I've been laid off, so can't afford to have it worked on by a professional...any help would be appreciated.