Q: 07 Honda Fit Code PO420. Car missing at idle when AC is on and has trouble accelerating, especially up hills, more so with AC on

Hi there.The catalytic converter has two oxygen sensors. One oxygen sensor is positioned in front (upstream) of the catalytic converter and the other oxygen sensor is positioned at the rear (downstream). If the upstream oxygen sensor is working properly, its readings should fluctuate from when the car is at operating temperature and when running in a closed loop. When the oxygen sensors have readings that are similar to each other, it is an indication that the catalytic converter is not working as intended. If the voltage of the downstream oxygen sensor decreases, and begins to fluctuate like the upstream oxygen sensor, it means that the oxygen levels are too high and the Powertrain Control Module (PCM) will store the P0420 trouble code. This could be caused by a cracked exhaust manifold, damaged sensors or catalytic converter or electrical harness that controls the the sensors. It would be a good idea to have a professional mechanic complete an engine is misfiring inspection.