Hmm,

pulling the vac hose from the FPR creates a vac leak directly into the throttle body area ,
so it should raise idle, mine does.

Maybe you already have a leak someplace and the computer is trying to compensate, creating a rich mix.
Unplugging an injector leans the air/fuel ratio back to normal range in your case.

I'd probably start by checking the bellows hose, remove it to check.
Then try find an air leak(vac leak) with some propane or ether.

Do the plugs shop signs of rich running?