Do you have the Volvo service manuals for your engine? If you post a serial number, I can tell you what one you need.
You really need the Volvo manuals ----- they have most of the info you will need. And for a problem like you have it's very difficult for me to help you if you don't have them.
The balance test is best done under load @1500-1800 rpm. And really isn't a valid test done out of the water.
At this point your doing tests and replacing parts in no logical order. That usually makes the job longer, costlier and can complicate things when you replace a good part with a new not so good part.
AllDodge "Can also disconnect throttle cable, then connect scanner and with the motor OFF and key ON, rotate the throttle slowly and watch the change" yup, I don't disconnect the cable because I like to do tests as close to real world as possible. But if your scanner cable isn't long enough, that would be another way.