Yes, I counted code 58 3 times in a row about 3 different times. When I pulled the TB, yes, I pulled it as a unit. I just removed the 2 nuts and 1 stud at the SC, removed the throttle and cruis linkage, and unplugged the electrical plugs. I put everything back as should be with new gaskets and injector O rings.
I'd really like to get to the bottom of this because I am putting headers on one of my Z28'* on Friday and will need something to drive to and from the parts store for those unknowns....