Manifold part name?

It's a vacuum switch , the 'AC' is for AC / Delco , and the 'carberator' (sic) is a throttle body.
The switches function is to regulate the flow of vacuum , and I am thinking it is the one that operates the trans kick down , though I may be wrong there.
You can get the whole upper manifold from a salvage yard for cheaper than replacing the switch...
Hollander part number 329-1488 , $15.00 .
The 3.1 was a common engine used in a whole bunch of GM cars so availability is there.
Call a salvage yard and ask for that number ; 329-1488 , and you'll get a better deal than just asking for a manifold because it will save them the 'trouble' of looking it up.

Don't know your zip , or I would include a link and pricing for your area on one.