I'll stipulate to the above.
Just wondering, if the fuel tank vapor hose is disconnected, then why is the tank building pressure?
Same thinking here. The famous rotted hose would just vent to atmosphere ????? Unless something crawled up there to block it. Archive pic:
I replaced the EVAP solenoid on my last FWB when I was getting a hissing cap, and all better. I read nothing above referencing that. I just got a new one figuring a perfect case of 'throwing parts at it' while also qualifying for a 20yo reg. maint. item. There's some parts of a drive cycle when it's energized to draw vapor. If that happens to be at startup it should be simple to check current with just the key on ????
Final thought: Most erryone on here knows not to 'top-off' as it chokes the vent tube and/or loads up the EVAP sucker tube so it can't draw? Either could be cause of hissing cap.