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I chased the P0422 for quite a while, and was determined that I would not spend the $1300 for a new catalyst. Very frustrating.
Along the way I found and eliminated potential contributors.
As I did, the symptom became more specific... driving at low RPMs during the warm up cycle.
When I kept the RPMs up by keeping to 2nd and 3rd gear until the temp gauge reached normal, I avoided the CEL / P0422.
This led me to try one more thing... re-torque the intake manifold bolts.
Low and behold... a bolt at the end of my XC's intake manifold (the one that you can see when you are staring at the engine from the front of the car that also has a bracket that holds the vacuum hoses)was 1-2 turns loose!
I have driven 2000 miles since tightening, and I have not had a recurrence... my mileage is solid 28mpg on highway and 26.5mpg overall... which is between 3 to 5 mpgs better than in a long while.
My analysis says that the addl air leaking into the intake was driving the ETM crazy. Driving at higher RPMs uses more air (and gas), and the percentage of extra air was less... something that the ETM can adjust for.
I'm now delaying looking for a new car for a while :-)
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