The plenum plate gasket blowing isn't a matter of "if", but "when". Chrysler, in all their wisdom, thought it wise to put a steel belly plate on an aluminum intake, so you can imagine what the difference in expansion/contraction rate between the two metals does to the gasket in-between. You can try and go after the O2 first, but if the plenum plate upgrade is needed and you're consuming oil, thus goes the sensor and eventually your cat (if you still have yours). It does sound like your IAC needs a good cleaning, however definitely keep the plenum plate issue in mind.......