How can I limit the autoscaling of gnuplot, so that, as example for the y-max, it is at least a certain value and it would autoscale up to fixed \"limit\"?
From loo
In this case, you could filter the data and let gnuplot do it's normal auto-scaling:
set yrange [*:*] plot 'mydatafile' u 1:(($2 >= YMIN && $2 <= YMAX) ? $2 : 1/0)