The 2 adjustments on the throttle bodies keep the throttle plates from closing all the way. The adjustment are the stops for the throttle plates / idle rest adjustments. The throttle plates need to be slightly cracked the same amount for balanced idle mixture, they also need to be slightly cracked to keep from binding coming off of fully closed. When carbon builds up on the plates, it will cause changes in idle mixture, it can also cause the plates to require added pressure to open, this causes kind of a snap when the plates crack open making it difficult to take off smoothly. The only other adjustment is the one in-board of the drivers side, this adjustment sync's the linkage to pull both throttle plates equally. None of those adjustment should require changing with stock throttle bodies unless someone before you made a change. Changing the adjustments on the throttle bodies will only change how far open the throttle plates are when not applying throttle, this adjustment does not affect performance when applying throttle, but it will effect idle mixture and the range of idle adjustment possible at the idle control valve. The balance adjustment on the drivers side linkage can and will effect performance because it is what allows both throttle bodies to pull evenly.
