2000 Toyota Corolla won't start

Cleared and check engine light came back the next day. Will be checking in a few hours to see the code

Would an improper terminal connection to battery cause a p0300?

@Yosemite

Still a P0300 code.

I look at the monitors and everything was ready besides Catalyst, evaporation system, and oxygen sensor.

Opened up the hood to see if I could hear any hisses for leaks and I cant even tell, its way too loud. I did hear something similar to hiss though.

1100 rpm on idle