Right on. Be careful though because that manifold is plastic and it's not metal-reinforced. It's stout, but still...

Please let us know what you find. Pete

OK I just thought of something else. When I had my intake off, I accidentally broke off the plastic hose fitting on the botttom of the intake manifold where those two hoses connect (the hose to the throttle body and the hose to the PCV system housing down by the power steering pump). Sucker just snapped right off due to being brittle. Friend of mine who was an indy shop owner said this happens with some frequency on these cars due to the heat and age making the plastic brittle. He said to clean it real good and glue it back on with JB Weld because the alternative is a new (or salvage) intake manifold. So I did. I have not run it yet so I don't know if that fixed it or not. SOOO I am thinking when you did your hose replacement you nay have cracked that hose fitting because that hose fitting is located right in the area you are talking about, i.e. between cyl #3 and #4. There may be a crack there that is causing the vacuum leak. Try your carb cleaner spray trick again, only try it in that area and see if that makes the motor smooth out.

Also spray the carb cleaner around the injector nozzles - maybe one of the injector o-rings is leaking. Did you replace the injector o-rings when you had the intake all apart for the head gasket job?