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I've got an 03 EX MT with 125K miles on it, and I've been doing some of the bigger maintenance jobs on it lately. I've also been monitoring the sensor readings, and I have noticed the long term fuel trim is running 2-3% rich. I've also monitored the primary O2 while driving after the engine has warmed up, and it rarely drops below 5%. Do these cars typically run this rich? If so, does anyone know why the ECU decides to do this? My cat recently went out, and I am trying to investigate what caused it. I believe the cat is bad because I'm getting an P0420, I haven't found exhaust leaks, and I've replaced the O2 sensors. Maybe it was just time for the cat to die, but I want to make sure. Also, what is a normal temp for the engine to reach? Mine is right at 190 F.

Also, when I pulled the old secondary cat it looked exactly like the primary, but with a shorter cord. So possibly a primary sensor was put downstream, but I am not sure. It was coated white when I pulled it, not sure what this means. The plugs don't look like it is burning oil, but I don't claim to have a trained eye. They're definitely not wet, though.