[T3] Weird Idle Dips, Suggestions?

[Toadpipe]

For several years now my 69 square does the strangest thing when idling 
for about the first five or so minutes after starting up then runs 
normally.  It revs up to idle then down to near stall then right back up 
with about one second between the peaks.  Does this only while idling, 
runs normal if I touch the throttle at all.  What could fix this?  Is it 
a sensor issue or something?  I can't seem to figure it out, but the up 
side is it doesn't seem to be a huge issue, it's just annoyed me for far 
too long to allow it to continue.


Toadpipe