But Mad North-Northwest
Join Date: Sep 2003
Location: SF Bay Area, CA
One thing to bear in mind is that fuel pressure should not be constant. The regulator maintains a constant ~36 psi pressure difference between the fuel rail and plenum. So if there's 5 psi plenum vacuum, the fuel pressure will be 5 psi lower than spec (i.e., 31 psi).
That's why you're seeing the fuel pressure drop when you snap the throttle closed: you get a spike in plenum vacuum and the fuel pressure goes down to match.
This wouldn't explain your fuel pressure steadily going down at idle, though. If I'm understanding your description that doesn't sound normal at all.
1963 Giulia Spider (1750 engine)
Former: 1987 Milano Gold