FITV, maybe coolant temp sensor. The FITV should close at a certain temp, and if it isn't then the IACV is trying to compensate for too much air going into the engine at idle. The IACV can only compensate for a certain amount, so it can make the idle hunt around like that. The fact that it is doing that once it gets warmed up narrows down the possibilities quite a bit. I agree that it could be air in the coolant lines, but the FITV itself can also go bad. Have you taken it out for a drive to see if it has any other problems?