well if your o2 or something else related is the problem, you should be getting a check engine light which you can go off of to pinpoint your problem.... Im not sure if the IACV would cause a check engine light.... If you have a check engine light on I suggest taking it to a shop that can decode it and let you know what your problem is and go from there... Also, dont rule out other things... It could be something as simple as a fuel filter or something along those lines.... When was the last time your fuel filter, cap and rotor, plugs, and wires were changed? basically when was the last time you had a routine tune up???