A good way to check that is take a small propane torch, unlit, and open the valve slightly and wave it all around that intake tube. Idle will change if it sucks in the propane through a leak. My T has alway idled around 550 since I bought it w/60K on it. I would think low fuel pressure would be more evident at high RPMs when it really needs the fuel. It is possible the pressure in the line is bleeding off between starts but that should go away once it has started and pressure comes back up. There is a pressure regulator in the system that also keeps it charged. Could be leaking.