2015 XC70 P0420 with CAT pics, troubleshooting assist

I noticed my idiot temp gage on the dash hits normal temp at 149°f. At idle I slowly brought up the RPMs to 4700 until OBD2 showed 212° F. The idiot dash gauge didn't budge from centerline. Not uncommon.

However, my ride to work this morning at an ambient temps of 32°F, my OBD showed temps at 178°f to 182°f on the highway, 65mph and 20 minutes of driving. Downshift a gear and temps went to 188°. The dashboard temp gauge of course was normal centerline

Idling the temps are 184 right now with ambient temps of about 70°.
 

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EVAP codes wouldn't have anything to do with a bad gas cap, perhaps, would they?
 
Fully warmed engine at steady idle, MAF reading jumping from 3.0 to 4.0 does not seem right to me. Should sit close to 3.0. I ain't no expert. Maybe someone here knows if this acceptable but my cars don't do that.
 
Fully warmed engine at steady idle, MAF reading jumping from 3.0 to 4.0 does not seem right to me. Should sit close to 3.0. I ain't no expert. Maybe someone here knows if this acceptable but my cars don't do that.
Good point. I recently found a vac leak that has been corrected since the scan pics were taken.

Will be ordering a new T-stat/temp sensor combo kit. May not be related to the P0420, but sweedspeed and other Volvo sites highly recommend changing T-Stat/CTS combo unit between 100-150k miles. Volvos of this vintage have a unique thermostat design.
 
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I installed the new downstream O2 sensor. Its been about 300 miles since, and the voltage in the downstream O2 is relatively stable, for the first time since i started tracking this issue. No stored or pending codes.

New coils, plugs, thermostat and hose on order from FCP.

No noticeable oil consumption, currently running M1 0w-40 FS and 2 bottles od rislone engine treatment. The sump holds 8 qts, so not really double dosing.

This likely would have been resolved by simply replacing O2, but glad I went through the cat cleaning process before changing the sensor. Along with inspecting everything, testing, cleaning, etc.
 
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