1) Thrust has to be increased because engine bleed output pressure at IDLE power is small(as you noted below 30 PSI).
2) ASU(or ground pneumatic cart) has to be disconnected(by ground crew) before engine no.2 start for safety of the GROUND CREW. In 737 ground crew's interphone jack is located on the right side of the airplane(in front of the engine no.2).
Hope this helps
