... the other side of these equation of lean running due to vac leak
[ unmetered air] is a simple check of the fuel pressure regulator.. a bad one will cause the same condition/codes , but on the rich side...........
Best test for this is fuel pressure gauge at test port, but a simple quicky indicator is to pull the vac line off pressure reg. and see if there is gas /fumes in the line.. if so , the reg. is ruptured [ allowing both high/unchecked pressure to injectors and unmetered fuel sucked into intake through the reg vac line.