The ol 11's idle has always wandered a bit when it's hot but now the engine is making a rare "pop" sound, like a backfire from time to time. No dramas under power but at idle it's starting to run like a hairy goat. Two days ago at the lights it just DIED completely, like I'd hit the kill switch. It started straight back up but I was between two cars and it could have been...

if the light had been green.
I did the plugs a few weeks back "new ones" and put a K&N filter in the airbox, any opinions on this roughness I'm experiencing??