Need help fixing my car?

1989 Nissan 240sx automatic 260000 miles fuel injected

Car wants to stall when first given gas.at a stop to about 2000rpms it wants to stall.but after those rpms its fine.rpms drop drastically all the way down until it stalls if I continue to press the gas.but if i let off as rpms drop it catches itself and acts normal until gas is pressed again.car does it in every gear where rpms are low.but after it gets past the low rpms I can floor it to redline without a problem. Car has check engine light codes for 45, a leaking(yes leaking) Injector and 23,a bad throttle position sensor.both were replaced and tps was adjusted correctly and still has the same codes.check engine light turns off at random and when it does car runs a lot worse than before.I have gas in my oil and spark plugs were black before replacement.car does not have excess exhaust fumes

Replaced fuel filter, o2 sensor, spark plugs, tps ( when disconnected runs a lot better), and checked the fuel pump and it seems fine.if fuel pump was bad wouldn't it not let me floor it after the hesitation? It will rev to redline very easily after the hesitation.maf sensor was checked and seems fine.car won't start without it? Or it won't redline? Correct?

Could these symptoms be a bad fuel pressure regulator? When I turn the key to on, but engine is not started, I can press the throttle cable and the fuel pressure regulator makes a electronic hiss or some sort of whining at about 10-15% of full throttle.almost the same amount of throttle that makes the car want to stall.before that amount its fine, and after the 10-15%, its fine.

2 days later today--- check engine light turned off but still runs horrible.yes it does have gas

Need help ASAP!