Plenty of crank but starts hard

The car runs great other than, more often than not, yet not all the time, it cranks over but
does not start until you stop cranking it, turn the key back and try again. Per
our local mechanic, it did not show any diagnostic issues. There was a loose
clamp for a vacuum hose that was tightened but still started hard the next day
after it was looked at. Any ideas before we just start changing things in a trial
and error fashion. Thanks for any assistance. We bought this vehicle
new three years ago and drive about 30,000 yearly (90,000 on vehicle now. It has been
starting hard for six months to a year.)