Hy,
many many thanks evreybody gave a suggestion to solve the problem. I,ve tried to take out the float but no way, i tried to take out the delay but no way. For Marco_c thanks for your code, i tried but again nothing. As i wrote if temp runs alone is perfect, with the rh sensor start to jump. Strange is that the first reading is perfectly correct, then from the second data wrong numbers. Some time the correct value appear. I definitely think (and hope) an external power is needed.
Thanks again.
Andrea