you will need access to a co meter. and then what could do is adjust the co by turning the adjust screw on the ecu to get the level down. if it doesnt drop you may have a problem elsewere.
but MOST important put the adjust screw back exactly to where it was by the same amount of turns and co level.
this is just in case it was there for a reason although it should not be that high for idle .if your not happy with this level get it checked out by a tunning specilist