What you described is exactly what I am dealing with right now as well. I have done many searches trying to find an answer to this problem. I cleaned the IAC and the problem came back about a week later. I just bought a new IAC this evening and will install tomorrow. I did read somewhere that if you have done the TH fix your hole diameter may be too small. I remember a few years ago when I did this fix I had to keep enlarging the hole. I will remove the TH fix and see how that plays out. But definetely, the car runs very poorly with the A/C on. I just installed new fuel filter, air filter, cleaned MAF, cleaned TB, all new O2 sensors, and no vacuum leaks. New IAC is next. Other than that, I am stumped??