Highly unlikely both of your 02 sensors failed. they are probably reading a code because your engine is running outside of what they can measure--either way too lean or way too rich. a MAF issue could do either of these, but probably wouldn't cause hissing. Vacuum leak could cause it to run rich and idle rough. Although honestly I know alot of crossfires tend to idle up and down a little bit, the electrical system isn't the greatest in the world in the car. Lights and AC load changes can definitely cause idle peaks and valleys.

I think they sell smoke generators to check for vacuum leaks don't they? maybe rent them? Perhaps some dry ice is a good idea, or some other way to make some haze in the engine, that's the easiest way to find a leak.