Rough idle

I have a 1992 miata w/ a 5spd. The car runs fine on the Highway.
It tends to idle a little low and on the rough side. Also, when I am driving the car and come to a stop at a light, the idle drops where it wants to stall, and has, then it will come back up again. It feels like it wants to stall.
All ignition components are new.
Any ideas?
Thanks,
Dennis

weak battery or alternator can have this affect sometimes. look here http://forum.miata.net/vb/ and try the search feature.