I have a 2007 RX8 that was getting IMTV Stuck Open CEL. I swapped out the SSV to the updated part. When removing the the control valve and pipe circled in photo 1, the back nut was rounded off bad. I used a twist socket to get it off but it turned out that it wasn't just a nut like I was expecting but this little beauty in photo 2. There also wasn't a control valve gasket there. I completed the SSV swap but can't crank down on this bolt/nut because it is rounded off so badly and the part is listed as being a nut and not a bolt. Suggestions?

 

That's a stud that backed out with the nut.

Carefully take the nut off.... replace the stud... and put a new nut back on...