I ordered brass plugs from Amazon and also tried the ones sold by Home Depot but none of them fit. The opposite hole has some sort of rubber plug. Any suggestions on sealing this hole?

Howard

Looks like part of a UFO. But if it's the back of a Z car intake manifold then it's the water inlet / outlet for the manifold heater pipe. It's probably BSPT like everything on the balance tube, engine water hose barbs, and fuel pumps. Possibly metric. Don't know because mine has a part of a rusted out "aftermarket" connector stuck in it, even the mechanic couldn't get it out (with the engine in the car".  Mcmaster-carr has a good selection of BSPT. MSA has something for that, they called it a "water valve" saw it on the site yesterday. Maybe it's for running a water tube around the back of the engine. Nice photo.

If it doesn't have any pressure could you put a rubber plug in first then top off the hole with a JB Weld type product?

Stanley's correct.  It's the port for the coolant transfer tube that links the front and rear intake manifolds.  A rubber O-ring is used at the base of each hole to provide an additional seal.  These holes are tapped for a BSPT (British Standard Pipe Thread) fitting.  That's not a metric thread, by the way.   The threaded plugs you ordered from the Amazon supplier probably use the American pipe thread design.  They won't work (as you've discovered).

Given that someone has already removed the coolant transfer tube (and thrown it away?), it appears likely that your car has this secondary coolant circuit completely disabled (it's designed to assist engine cold start and warm-up and many Z owners have found it unnecessary for the climate conditions where they drive) .  As such, there's doesn't seem to be any need -- other than aesthetics -- to block off these open holes at all.  The coolant passages within the intake manifold don't connect to any air passages, so whether these coolant ports are open or blocked should have no effect on the operation of the engine.  That said, if it was my car, I'd find the correct BSPT fittings and install them.  You'll need two plugs for each manifold (total of 4).

Wow thank you everyone for the information. Yes I was worried it was open to air. I will close them for aesthetics.

Howard

Edited February 7, 20179 yr by 882993md