Codes 0431 and 1521

[Mikemilli]

OK heres situation: For the code 1521 i replaced both vris solenoids and for a few weeks didnt throw a code until this recent 0431 code but that could be because i didnt check since the mil didnt come on. So im thinking maybe its the PRC solenoid anyone had any of the same issues?
As for the 0431 code i replaced both o2 sensors on bank 2 and im still throwing the code. I really hope its not the cat .. Anyone that has dealt with this or could give me some guidance would be greatly appreciated. Other than that car runs good besides guzzlng gas.

[yel-low]

If you've replaced the solenoids (although they seldom go out), the next step is to do a vac. check off one of the manifold nipples next to the solenoid bank. Those lines that were once soft and supple become baked and super brittle. They expand a bit from the intense heat and fail to make proper seals on the solenoid/check valve/dynamic chamber nipples. On some of my cars the lines are free to slip on and off. I'm often too scared to mess with them much because of how brittle they have become.
There is also a small check valve on the line. Make sure it is still operational and not toasted. Lastly you should check and make sure those accumulator chambers still hold vacuum pressure. They also tend to crack.

If the intake manifold has been taken off before I would double check all the harness ground points. There are a few inconspicuous ground spots on the bracket that the solenoids need.

As for the P0431 I would just pull the exhaust manifold and look down into the cat to see if it's melted and look into your exhaust ports on the head to make sure you don't have lots of carbon. That can be an indication of improper air/fuel ratio due to leaky injectors, bad plugs, or gross vac. leak.