I have been suffering with "kangarooing" in the Sportster for months. I thought it was either my crap driving or something needed setting on the tuning side.
It turns out to be nothing more than throtle cable adjustment. Over the last 18 months it must have streched slightly leaving just too much slack in it on idle. A quick adjustment and hey-presto no more kangarooing!
I've not had Kangeroo'ing nor high idle.............
.......... but that's probably because the horses in my 2 litre are so knackered they haven't got the energy to do either