The idlepc value is very important to dynamips and it is both image and often CPU dependent. There is no "magic"value that will work for all images and all CPUs so this is why I'll show you a quick and handy way.
Also don't be disappointed, some values do not work well but idlepc gives you several. For example in my example below #6 didn't help at all but #7 got me down to about 6% CPU from 99-100%.
*Befo........