Is there any terminial command I can use to set the polling interval on an elm327 device? I know that for example obdwiz allows setting the polling interval through it's graphical interface, but I want to do it manually from the command terminal.
So it seems that it's only Elm327 adapters that use a FTDI serial to usb adapter chip that have these latency problems:
The FTDI can’t send a USB packet to the computer for every byte that comes from the Arduino’s microcontroller. Instead, it stores the serial data in an internal buffer and only sends a USB packet when the buffer is full, or after a period of time has elapsed. This period of time is determined by the FTDI Latency Timer, which is the reason why FTDI chips can give bad latency characteristics.
On Linux & Windows, the default latency timer setting is 16ms.
So basically, taking into account both the data request and the response you are automatically taking a 32ms hit round trip.
Luckily, the latency can be reduced to 1ms. The above link explains how to do that for a variety of operating systems.
The ForScan software has a visual tutorial on how to do it in Windows.
Polling interval is simply how often you request data from the port. There is a hardware side baud rate that you must meet (probably 38400bps for ELM327) and usually you cannot change that as it is determined by the protocol.
The software you mentioned simply lets you set the rate at which you send/receive data bits to meet this requirement (there are multiple standards). If you use a terminal application then it should let you set the baudrate.
EDIT: If it actually lets you set the polling interval then it simply changes the frequency at which it inquires the port, it is fully software dependent.