The search for missing boost..........and vacuum

I just started driving my 90 (anniversary edition) and I’ve come across a few issues and thought I’d ask for some advice.
At idle I maybe pull 10-12 in of vacuum and at most I’m able to make 7-8 pounds of boost according to the stock gauge(I realize the accuracy of the gauge may not be awesome). This car has been my grandpa’s since 93 but he’s since passed so I’m trying to figure out all the issues and quirks of the car. After doing some reading I’ve decided to do a leak test tonight. I figure I’ll do it according to the write up in the faqs. I already have a compressor with a regulator, as well as second regulator. From what I understand, I’ll need a some type of fitting and nylon hose to attach to the boost gauge nipple.
Where is the boost gauge nipple? Does anybody have a better description of the fitting and the size of nylon hose needed to attach it to the boost gauge nipple?

I have another issue that I’m hoping is related. Most of the time it idles perfect but other times it oscillates between normal and lower than normal. Does that sound like how vacuum leaks manifest in these cars? Any advice would be greatly appreciated. Thanks.

check your boost gauge sender hose. could be rotted. i just replaced mine with a $5 kit from autozone.. sunpro i believe... i jsut stuck it inside the rubber nipple... (located on the drivers side, behind the plenum.. theres a green vac hose coming from it. just take the green hose off, put your nylon hose in there.. and secure it. i used a ziptie, and no problems whatsoever, i just replaced the rotted section, and used a vac line connecter to join them. you could also run it inside and jsut replace the entire hose.