Fix all of your vacuum leaks first before you do anything else. Once you have NO MORE VACUUM LEAKS, then reset the computer and try again. If it is still having misfire and fuel trim issues, then you need to spray along every parting surface. Throttle body to manifold, upper manifold to lower manifold, lower manifold to cylinder heads, etc....Also, the plugs, wires and distributor were not changed. only FPR and injectors.
Regarding the test. Do i test this around the plenum where gasket meets lower intake or lower intake? (This question may sound dumb after what I just explained the missing hoses lol).
If the engine RPM changes while you are spraying a specific spot, you found a leak.