Can't agree with the previous posts more, a trip to Marc Haibec's is in your very best interest.
Not cheap or quick, but it is your very BEST option.
As far as I know, there are NO shops in the SF Bay area that have even seen a LT5 much less worked on one.
That being said, if you're handy, have reasonable mechanical skills, tools and somewhere to work your car, here's all you will need to narrow down what you need to fix and give you a thorough understanding of how/what/where the secondary vacuum system does and how it does it.
https://www.corvetteactioncenter.com...nosis-482.html
A plenum pull is a rite of passage for many (if not all) a ZR1 owner.
Do not, and I repeat loudly, DO NOT drop your ZR1 off at the local Chevy shop and expect them to know anything about your car.
They will not.
It's almost a guarantee that they will make whatever problem you're having 10x worse.
Only Chevy master techs were allowed to work on the LT5 when new, and even then the policy was to diagnose whatever the issue was, yank the engine and replace it with a new engine.
No mechanic in any Chevy shop was ever trained to address anything deeper than regular tune up items.
30 years later, anyone that was allowed to work on a LT5 is now long retired.
I'll throw this out there, I'm not all that far away (Folsom, CA) and I could make room in my garage for your car for a few weeks.
I'd be willing to take her in for a little while and see if I can perform some magic for you.
Trouble is, I don't have a ton of spare time (am still working full time, *this close* to retirement but not there yet) and it might take a little while to diagnose and then acquire the necessary parts to effect the repair.
Nothing would happen overnight, expect the entire process to eat up a lot of Spring and maybe into the Summer.
Just so you know, the "BrotherHood of the Beast" is alive and well.
'Crabs