what causes rough idle and internal backfire?

What exactly is an "internal" backfire. Backfires are either through the intake or through the exhaust.

When i go to give it gas while in gear there is a "bang" sound that comes from inside the engine.

You have to mean intake backfire. That usually means an ignition issue. Check the plugs wires cap, rotor and timing.

I checked and replaced all of that except the wires. What could cause low fuel pressure? I canged the fuel pump and fuel pressure regulator.

What do you mean by "low fuel pressure"?
How low?
Is this a problem when running or rest pressure?
Does it hold rest pressure?

Ive been reading and regular pressure is supposed to be between 35-45 psi and mine reads 20 psi while running. About 10 psi in rest pressure.

If you don't have a restricted filter, try pinching off the return line and see if it spikes up. If not, you have a bad pump.

I bought and changed the filter and pump and it helped bring up the pressure a tiny bit.

Make sure you don't have a voltage drop to the pump.

My coil looks quite old and rusty. Could it be that?

Causing low fuel pressure? No.

This confused me greatly. My dad unplugged the hose from the map sensor that goes to the plenum and plugged it and put a vacume gauge on the map sensor and put it to the right pressure and it ran perfect. As soon as the hose was back on the map sensor, it ran poorly. Whys that?