Because the IBM web site is rubbish I cannot find if you adapter is an onboard serial port, or a PCI adapter serial card.
The onboard serial ports are limited and do not comply with the RS232 standards.
If you need to use anything other than a terminal, and it seems you do need a little bit beyond simple serial console connection, then you'll need to buy a PCI RS232 adapter and use that, if you are not already.
HTH