Previously you "fixed" the problem by manually restricting the fuel return line to the tank thus increasing pressure to the injectors.
Does that still work?
If so, it seems to me that would strongly indicate a pressure issue and not much else.
The throttle position sensor controls the amount of fuel to the injectors with pulse width modulation but I don't know that that is your problem. The sensor provide 0 to 5 volts back to the computer letting it know how wide open the throttle is.
Keep in mind that your fuel pump in the tank receives voltage through the oil pressure sender when the engine is running so if there was a problem there the pump might only run occasionally.
I might start wondering about whether the engine computer is somehow monitoring that area and has a problem. Maybe remove battery cable for an hour or so and let the computer clear itself and then start all over. But that's a wild a** guess.
