Arduino Nano AtMega328 Interrupts and Communication

I have an Arduino nano using the atmega328 chip, I bought it recently, but I'm not sure which bootloader it's using if it would even matter in this context. I'm trying to use the Arduino to communicate with a raspberry pi. Both are wired to a pc power supply, and I've tested that they have a common ground, although with about 80 ohms of resistance between them. I'm having two problems, but both may be fixed by the same solution (I'm hoping fixing interrupts will allow me to continue). I was using Ben Eater's programming for the receiving programming from his reliable communication series (Reliable data transmission) to try to send/receive codes using binary, but my interrupts were having issues, either firing randomly for random intervals of time, not firing, or firing constantly, most of the time without an input signal.

I then went about trying to use Nick Gammon's solution after failing to implement other solutions I found on the forums, and it also either didn't help, or I didn't understand it well enough. Very many of the posts explaining how to fix the issue seem to be a little out of my level of understanding, so that's definitely where a problem lies.

Trying to avoid the problem and testing another solution to be able to communicate with the Rpi, I've run into the issue that the Arduino seems to be receiving a signal even when nothing is connected to the pin. I'll include my code for the Arduino, but I can also include the raspi code if anyone wants it for reference, although it's relatively similar. It's written in mu using the rpi.gpio library. The code is pretty barebones since I'm still relatively inexperienced programming for the Arduino, and because I only need it to read a signal, and send one when one is read. Here's my current code:

#define RX_2 2
#define RX_3 3

void setup()
  pinMode(RX_2, INPUT);
  pinMode(RX_3, OUTPUT);

void loop()
  if(RX_2 == HIGH)
    digitalWrite(RX_3, HIGH);

edit: I realized I didn't explain the issue I'm having with the code I sent well. Pin 3 sends a high voltage even when nothing is connected to pin 2. I'm assuming the issue lies somewhere in having the loop run a test constantly, but it was the best workaround to not having access to interrupts that I could come up with.

Pin 3 sends a high voltage even when nothing is connected to pin 2. I'm assuming the issue lies somewhere in

Not surprising if 'nothing' is connected to the pin 2, its floating, sometimes it will read high, sometimes low.

Input pins need to be set high or low, not left floating.

Aight, I set it low and it seems to be working. 3 isn't sending high anymore. It's nice to be able to continue with some sort of solution, but not having working interrupts is kinda annoying. Thanks for that info