HondaHell

I have a 1998 Honda Civic EX / 1.6L / D16Y8 SOHC VTEC 130K mikes that keeps throwing the Mystery P0505 DTC code. We have taken off the CAT inspected it / not clogged / replaced both Bank 1 + Bank 2 O2 sensors / upstream & downstream with brand new sensors / replaced the Fuel Filter with a new FRAM / Autozone Duralast does not fit the banjo fitting properly @ hint !!! / replaced all 4 sparkplugs / new wires / replaced the IAC motor / TPS sensor new / MAP sensor new / Thermostat new / Purge Solenoid new / changed out the PCM / cleaned disgustingly dirty fuel injectors / checked and readjusted timing with timing light / measured Engine vacuum @21 psi @ idle on intake manifold. It will idle OK, and cold it is about 1500 RPM and will pulloff down to 850 RPM when warm / I readjusted the Throttle Body needle valve / 1/2 turn out from bottom ( that seems too closed ? $uggesting a vacuum leak or IAC issue which it has P0505 code, but its not the IAC motor / its brand new @$130 ouch !!! )
Its not the wires to the PCM from purge solenoid either - pins 7 + 11 on PCM, they checkout, and I hung an oscilloscope on the connector to measure the control pulse and saw it working. So I am down to replacing the fuel pressure regulator + fuel injector filters + seals. It could be a related system problem with the PSS switch ( power steering pressure switch , pulling its connector throws a solid P0505 every time disconnected ) or even a dirty VSS sensor ( vehicle speed sensor on the manual transmission - low transmission oil ? ) I followed Eric the Car Guys procedure on bleeding the radiator and refilled it with a gallon of brand new Antifreeze.
It will sometimes throw the P0505 code at idle on the driveway, and after enough miles driven the CEL / MIL light with come on with a hard P0505 and store it as a permanent DTC. I can clear the PCM / codes / Pull the 7.5 @ fuse under the hood, nothing makes it go away. The car idles good / drives OK too / but it will eventually stumble and when it does, I notice the timing advances from 12° to 16°, so I'm suspecting the Fuel Pressure Regulator, as the O2 sensors voltages also correspond to the lean / rich schizophrenic responses...ANY HONDA TECH geniuses out there will any GOOD idea$ ? Let me know...