vacuum signal comes from the branch on the idle speed regulator pipe - pull it off the FPR and see if there's vacuum. other than that, you can't really do much else without kit.
how about manifold vacuum leaks ?
or air flow meter death ?
so it's just misfiring at idle only and not when you're driving. Even at low revs / high load ?
I know the EGR valve is leaking 'slightly'.  It blew a couple of bubbles when I jet washed the engine bay a few months ago.  Not related though otherwise it would have misfired way back then.
I have replaced the AFM with a known dodgy one!  The misfire didnt get any worse/better, so stuck mine back on.
Misfire happens every 10-15 seconds on idle, sounds like just a single clyinder not firing but only a tiny blip.  It corrects itself after (what seems to be) a single cycle.
Under HEAVY load, it misfires a lot.  Ease off tyhe throttle and all seems to be perfect.
I'm also using a LOT of fuel.  Average is 17MPH at the moment, it's normally around 25-27MPG average.