1981 928 intake refresh
 

I've had a separation of the airflow sensor and boot and want to clean the plenum. I am not sure of how to remove the upper plentum. It seems to be really on there.

I think I might start by ordering the replacement rubber parts. A premade vacuum hose harness is a big help. When I sent out my injectors for cleaning, I sourced two extra injectors and sent all 10 to be cleaned and flow matched, and good I did as a couple were still low flow after several cleaning cycles.

If you are talking about the fat cast tube between airflow sensor and throttle body, there are some rubber with threaded metal stud stand offs, plan on replacing those as well.

Three of these rubber things, I think. https://www.pelicanparts.com/More_Info/99970326100.htm?pn=999-703-261-00-OEM&SVSVSI=0998&DID=7712