This is what the OBDuino is doing, just connect your LCD as the diagram, and load the sketch in the Arduino IDE, compile, upload
obduino32K.pde - opengauge - Project Hosting on Google Code
uncomment the
define ELM and comment the
define ISO before compiling.
Also I don't remember if you need a crossed cable between the serial port of the Arduino and the ELM327 interface or a straight one!