Found the problem. Ended up being a sneaky ground underneath the intake manifold cover that I didn't know existed until I looked at the wiring diagram. It was completely loose and corroded. Thank you for your help, guys!Great advice. I downloaded the wiring diagrams for the car so I'll try to look at all the grounds I haven't touched yet. I will say though that I have already looked at the grounds associated with the ECU/micu and such.
One other thing (and I'm really just saying every small thing I've noticed at this point) is that the right bolt that mounts the ECU to the chassis was very rusted at the bottom, while the left bolt was not. Is this coincidence? Is the ECU grounded through it's chassis and the car's?