So from your setting, the screw was just barely touching the throttle arm when set correctly?
This is why I am asking. I purchased an underdrive crank pulley. I installed that the other day, along with a new alternator with a smaller pulley, to help with the charging. When the car is in park or drive with no lights on, the voltage is fine. In drive, with fog lights and/or headlights, the voltage drops down into the 12's. Once I start moving, the lights brighten and the volts go back up.
I thought getting the smaller alternator pulley would have helped with any problems. I guess it is not worth having an underdrive pulley on a daily driven car if it is going to cause voltage problems like this.