Mitsu TPS's are very VERY fickle. They need to be pretty much dead on when setting otherwise it will "idle hunt" (revving up and down at idle). It will also throw off fueling and other settings. I usually tell people not to mess with it unless they absolutely have to.

The throttle closed position (0%) is actually a large range. If you don't have it dead on, it will add problems. If you have a bad TPS already, you will just make things worse. The best bet is to replace the TOS and try setting it if you are certain it is bad. The TPS doesn't randomly adjust itself, so if it is throwing a code because the TPS is bad (not in conjunction with, or a resulting code based on another problem), chances are it's just needs to be replaced, not adjusted.