A leaking plenum will screw up your o2 sensor and cat.

 

true. the only reason i dont fully think its a vacuum leak is because the scanner i checked it with said that the map sensor read a constant pressure at idle and the fuel trim stayed constant as well, both of which would probably fluctuate with a vacuum leak that caused it to run rough

 

Some ppl chrome them before putting it in. I wouldent though, lol.