I was deleted in the crash, so I'll try again. After over 20 hours of effort, removing and testing almost everything associated with fuel and vacuum, I discovered the engine coolant temperature detector (the grey one) was bad. No codes even though it was registering millions of ohms resistance. My 2000 vehicle would start and idle high, about 1500 rpm. (mine did not drop when tapping the gas so this may have been a different problem than yours). After about 30 seconds of running, it would not start again if I turned engine off. Needed to take off the thermostat to get to the detector. A $15.00 part solved my problem.
By the way, what I believed to be the fuel pressure regulator doesn't seem to do anything in the configuration where there is no fuel return line. It sits on the end of the fuel rack with a vacuum line connected to it, but does nothing to regulate pressure as far as I can tell. The 65 psig pressure I found in the system is the fuel pump pressure, as it should be if there is no return fuel line with a valve to control pressure.