92 DeVille randomly won't start, turns over
 

I have a 92 DeVille that sporadically will not start. The engine turns over but will not fire up. I had my dad look under the hood at one point while trying to start it and he saw sparks flying out of the distributor cap.

The last time it wouldn't start for me I had it towed to our mechanic, as soon as they got it off the wrecker it fired right up, no problem. They kept it for a few days but were unable to recreate the problem. They said it showed no codes and they checked the fuel pump and filter but there was no issue with those.

Anyone have any other ideas what this might be?