Long time reader, first time posting. I have a 2000 Outback with the infamous P0420 code coming up. It has been happening for a couple of months now with rough idling. Initially the CEL was turning on only when it was below freezing but I did not have a code reader then. I got a reader a few weeks later to find out it was the P0130 code. Assuming it was the front o2 sensor I ordered an OEM one. Within 30 miles the P0420 code appeared so I immediately ordered a rear OEM o2 sensor. Installed it and again got the P0420 quickly. I got my hands on some used OEM catylytic converters and the code still came up.
At this point I started digging harder on the forums and realized I should have been doing some more basic maitenance. I seafoamed (pcv, gas, and crank), cleaned throttle body and IACV, changed the fuel filter, pcv valve, spark plugs and wires (ngk), air filter, coolant flush, OEM thermostat. Still getting the code. I am pretty discouraged at this point and thought that my used replacement cat was bad so I swapped it with my buddy's 2001 legacy and we both drove a tank of gas with no codes thrown.
Some other info, oil (5w-30) changed and new battery within 500 miles, 87 octane non-ethanol always used. I tried using 91 for a tank and it held off the code for a bit longer than usual but still came up. I also tried a spacer on the rear o2 and it also held off the code a bit but came up around 100miles. I am getting around 22-26mpg with mixed city/highway driving. I would appreciate any suggestions as I've spent countless hours reading on here, NASIOC, and other Subaru forums.
At this point I started digging harder on the forums and realized I should have been doing some more basic maitenance. I seafoamed (pcv, gas, and crank), cleaned throttle body and IACV, changed the fuel filter, pcv valve, spark plugs and wires (ngk), air filter, coolant flush, OEM thermostat. Still getting the code. I am pretty discouraged at this point and thought that my used replacement cat was bad so I swapped it with my buddy's 2001 legacy and we both drove a tank of gas with no codes thrown.
Some other info, oil (5w-30) changed and new battery within 500 miles, 87 octane non-ethanol always used. I tried using 91 for a tank and it held off the code for a bit longer than usual but still came up. I also tried a spacer on the rear o2 and it also held off the code a bit but came up around 100miles. I am getting around 22-26mpg with mixed city/highway driving. I would appreciate any suggestions as I've spent countless hours reading on here, NASIOC, and other Subaru forums.
