highly intermittent idle problem

[Kiwi]

My idle had been  getting a little rough so i decided to mess with it a bit.  After getting it to settle in nicely around 1.5k i left it idling for awhile.  I go inside and i hear it die.  It didnt die slowly, it just stopped.
I starter her back up and all was well.  A few minutes into idling again it almost died but seemed to recover.
It isn't really slowing down, it's more of a stop and then it catches again.
It doesn't do it often , or in any pattern i can discern.
I did check that the fan coming on was not killing it, and it doesn't seem to be related to that.
i also noticed that the lights are not affected by this temporary stop either.
Where to start? what to check ?

[Night Vision]

does she stall before the fan comes on? or just when she's hot enough for the fan to cycle a couple of times....

[Kiwi]

It only seems to happen when it is hot enough for the fan to come on.  I watched the fan cycle on a few times with no side effects