1997 Ford Taurus 1997 Ford Taurus won't stay running

Earlier this year I had some issues with my car idling rough, and no power even with the pedal clear to the floor. I got my codes checked and I was getting a too lean code for banks 1 & 2. I replaced my spark plug wires, and spark plugs, and a new Mass Airflow Sensor. Then my codes went to banks 1 & 2 were too rich and there was a Camshaft sensor malfunction, and my fuel pressure was only 18 psi. Since then I have replaced the Camshaft position sensor the whole piece that goes into the top of my motor, my fuel filter, fuel pump, EGR valve, PCV valve, Throttle Position Sensor, both upstream Oxygen sensors, and I cleaned my Idle Air Control valve. Since then my fuel pressure is between 37- 45 psi. And I have fuel, spark, and compression, but the car will not stay running. When I start it up it will go up to about 1,000 to 2,000 rpms then die instantly. If I push the pedal clear to the floor sometimes it will rev up to about 4,000 rpms for a few seconds then it will die again even with the pedal to the floor. And when it does this sometimes it will backfire a little bit. But it will not stay running at all. I have has several people look at it and they have no idea what is wrong with it.