1990 ZR-1 cranks but won't start

[sdickens]

Car is my daily driver. A couple months ago I was Leaving work one day tried to start it, would crank but not start. I had it towed to my*mechanic, they tried to start it, but same issue.
They pushed it into their bay, set it up for diagnostics and then it started right up and every time after that.

Yesterday the issue came back. was out to lunch and when done the car would crank but not start. I got a ride back to the office and end of the day back to my car. It started right up.

Any ideas on what would cause this?

Thanks,

Sam