P0133 and P0420
I have been struggling with an annoying problem for the past 6 months with no indication of what is wrong, basically when it is really humid outside, or raining, after the motor has totally warmed up when I come up to stop lights, the car will start to idle very strangely, it sounds like the car is a cammed V8 and usually stalls if I let it idle strange for too long. if I blip the gas pedal once or twice it usually starts to idle normally. This normally comes up when coming to a red light, which is incredibly annoying.
Given that the car just passed 100K miles I did some regular maintenance stuff to try and track down the issue. I pulled the MAF and cleaned it thoroughly, I pulled the IAC and cleaned it with carb cleaner, sprayed the whole intake manifold down with carb cleaner while the motor was running to find any intake leaks, there were none. I also replaced the spark plugs with Autolight Double Platinums, did the ignition coil (there was a small crack in the resin) and did the spark plug wires as well.
The motor runs smoother now, but I still get this strange jumpy idle after the motor is fully warmed up and while I am coming to a stop, I also have noticed that when the motor is running below 2500 RPM sometimes I will get some "surging" on acceleration, the powerband doesn't feel smooth.
Today it gave me the codes mentioned in the title, P0420 and P0133. Is it common for the catalytic converter to fail on an SVT at this time? Or should I assume that the upstream O2 sensor is causing for a rich mixture which is making the cat not work as well as it should.