One more question: Those IDLE connections.. are using the server's resources?
To solve that problem I would need a Pool connection, right?
Would the pool connection solve that IDLE connections? But more important than that, are the IDLE connections using the machine's resources ?
Yes. There is no straight way to terminate the IDLE connections from the database end. You would need a connection pooler like pgBouncer which can help you terminate IDLE connections after a certain time.
It would be much better if your Application can terminate connections to the database.