ok, let 'splain it a little.
the injector offset is a small amount of extra pulsewidth that is added to the calculated "base" pulsewidth in order to correct for the fact that the injector does not open instantaneously. if you want xx grams
of fuel shot in, and calculate y miliseconds to deliver that fuel, the actual pulsewidth needs to be a little more, since the injector needs a little time to snap open.
the amount of offset required varies by the type of injector, and impedance/drive strategy and the voltage available.
now, the SD2 has several offset curves in it (the actual offset depends on the ignition voltage, so there is a curve) which is selected by the offset parameter, and you can adjust slightly from the preset curve.
if you set the offset to 25, you get offset table 2 (the 10's digit picks the table), and no 'tweak' (5 is the middle of the adjustment range) 26 is table 2 and a little more, 27 is a little more than 26, 24 is table 2, but a little less....
and so on.
some of this make sense?
the bottom line is if the offset is too small, the idle will be lean and the tip in will be lean. I tune the offset so that the idle is ~ reasonable then tune the tip-in after.
Bob