In Swedish, we have an idiom that goes, "to suck on the/that caramel [for a while]" and is used either when you need to contemplate a decision ("I'll have to suck on that caramel for a while before deciding.") or to try and figure something out ("He had been sucking on that caramel just as long as I had, but neither of us had an answer.")
I can't find a good English equivalent to the second meaning of the idiom, but I'm sure there is one. So, I need an idiom for trying/having tried to figure something out (without luck, so far.)