I'm assuming you're referring to the fuel pressure damper, not the regulator.... It's back by the firewall? No do not adjust it. It is essentially a very touchy secondary fuel pressure regulator and they're about impossible to reset once screwed with (get it?!
). It's supposed to have a plastic cover. The screw will move in and out as the engine runs because it's directly connected to the diaphragm inside... I've seen two where all the years of movement they've vibrated loose to the point of floating around inside the plastic cap... but I still suspect it wouldn't have happened unless someone broke it loose to begin with.