I have a 94 GSR w/ 128,000 mi, AEM style custom intake, everything else is stock.

So yesterday after driving about 30 min, I noticed steam leaking out from around upper part of radiator. I returned home, keeping an eye on the engine temp, it never got over half way to H, so i thought I was ok for on quick trip. Ran to the store a bit later, and after 5 min of driving the idle starts to fluctuate between 1000-2000 rpm only when the clutch is engaged or in neutral, when I am driving it seems alright. I have kept up with regular maintence and don't drive too rough. Anyone have suggestions?

I'm think an idle bypass valve and a new radiator? Any help would be appreciated.