High idle warm P0420

I have been experiencing high idle when downshifting from highway speeds. 2000-2200 RPM. Sometimes while I hold in the clutch it will slowly drop some. I have been using my BlueDriver to monitor fuel trim, o2 throttle position and engine temperature. They are running within normal range and throttle is closed, not hanging up. Had TB and iac off to clean up a couple months ago because of this issue and it didn’t resolve the issue. Seems as though it does this before and after it trips P0420. So I am wondering if anyone has had an issue like this? What would be causing the idle issue? Could a faulty misreading o2 sensor cause idle speed issues? I am also experiencing some bucking when it is warming up driving.

 

420 will have nothing to do with the high idle

 

My high idle was previously due to dirty IAC. It’s kind of difficult to clean completely. The metal piece that opens and closes needs to be totally clean all the way around. I had to actuate it manually and also used a 12v battery to help open and close it.

There are other causes of high idle tho.