My miss is gone

[Minn-Tex Lee]

For a year I have been fighting a severe miss. I went through all of the normal suggestions -testing pressure, soaking cylinders with various fluids, changing out the plugs, new coil etc. This year I was about to check for a broken valve spring.
I started the engine and sure enough it still missed for about 15 seconds and then it purred like a kitten. I took it for a 10 mile ride with no problem. My questions are these:
1) What do you think the problem was?
2) What are the chances the problem will return?

I was hoping to get a chance to use my new 4 trace 4 color scope to see if it was electrical but I guess that wont be necessary.
It did, by the way, go through a Minnesota freeze thaw cycle in an unheated garage.
Thanks for your thoughts
Lee