Would a bad fuel pressure regulator cause a car not to start?

Got off highway one day, car would not stay started at stop signs (at idle) "unless" I give it gas.
Changed air filter. Car ran normally for 2 days, then would not stay started at idle again.
After about every 3 days the idle symptom would go away, work fine for 3 days, then return. This went on for about
a total of one month. Then;
Adjusted the Throttle Position Sensor and car ran normally for about 1 week straight. Then;
Idle issue returned, but this time worse than ever. Looked under hood and noticed the Fuel Pressure Regulator had
malfunctioned and was sending fuel into it's adjoining vacuum line.
Replaced Fuel Pressure Regulator with one from salvage yard.
Now car will crank, but will not start at all?

This replacement (but used) regulator does not shoot fuel into the vacuum sys, but could it still be bad? How can I figure out if it is in fact bad?

I'm down to the Fuel Pressure Regulator or Throttle Position Sensor.

Any suggestions?

P.S. I opened the rail right above the fuel injectors; fuel DOES shoot out when I crank the engine. However, it does NOT come out when the key is in the "ON" position. Also, put spark plug and wire to ground and spark IS present.