Mine did this and I finally tracked it down. It ended up being that I had the adj to the throttle cable too taught on the slide bracket behind the valve cover post head install.

Adjusted it as per the service manual with a little slack and AFR's go full lean again off throttle

 

If neither of us have messed with our throttle cable at all your experience leads me to believe more and more that the ISCV adder could help us out. (same condition, too much air past the butterfly, too little vac)

 

Thanks Guys. I will attempt to tighten the throttle cable because this is quite easy and quick. If that does not have any affect then I will try to put my old airbox back. Thanks for the suggestions. I will post what I found after I get it fixed.

 

With my issue it was too tight (holding the butterfly open) I realized I needed to put a little slack in my cable and adjusted it as per the service manual. AFR's no longer stayed rich on decel and now go full lean again

 

I already had a bit of slack in my throttle cable. I did attempt to tighten it slightly, but I am still getting the rich behavior after clutching. It is quite strange because the AFR dips rich, then returns to very lean and then goes rich again. Since there are 2 rich dips this is confusing to me.