ye, it comes with a bit of an instruction manual, think most of its in japanese though :?
You can download one from apexi's U.S site though, it has a diagram of the GTI-R ecu, and tells you exactly where to splice the wires, virtually no set up needs doing (although i did faff about with mine for a couple of weeks after installing it
)
The hardest thing is knowing how to get the wires from the engine bay to the ecu (i used the grommet for the ecu harness), and also where to fit the pressure sensor takeoff (the left hand nipple on the inlet manifold is favorite), oh, and where to fit the controller itself (it's a bit bigger than you might think from the pictures).
As for what it does, kieron pretty much covered it, except, it doesnt show speed in kph, it shows it in whatever your speedo does (it just says kph on the screen), also, the most usefull functions that it has (although you may never use them), is the abillity to increase/decrease boost in different gears (usefull for reducing wheelspin in fwd cars), and the ability to increase/decrease boost for a given rev range (this allows you to run more boost in the mid range than at the top end, which is obviously safer).
It also has a peak hold which is good to see what your boost is doing, as is the 60 second playback (tells you if your boost is dropping off at any point)
The different displays are actually quite nice to have, i usually just have it on the boost gauge, but sometimes its good to know what your max revs/speed :evil: was