I can see the IAC causing the bad idle, but the loss of power until high RPM, I don't see how the IAC has any influence over that.
I have seen alot of threads on this subject floating around the forums, I think it is a common problem.
My opinion, if you idle bad and have trouble making power even at high RPM then it is an air leak or a fueling issue.
If it were an air leak downstream of the MAF the O2 sensors would be sensing a lean mixture for the ammount of air being detected by the MAF, the computer monitors for these types of disagreements and when they occur it sets a trouble code or turns on the CEL.
Change your fuel filter, put some dry gas in your next tank and see if the problem goes away, if not then I would suspect a problem with the fuel pump not making sufficent pressure or the fuel pressure regulator not allowing fuel pressure to build up high enough.
clogged exhaust system is not likely becasue it would have to be seriously blocked to make the car have trouble idling.
