97 grand caravan starts, but dies immediately

Occasionally, about 5 times over 3 months, the van will not start properly, twice in the last week. After it has been sitting for a
period of time, usually an hour or two, it turns over, fires, but dies within a second or two of starting. None of the instruments function when this happens, not even the gas guage. After sitting for an hour or overnight, then it will start and stay running, like the problem never happened. So far the problem has not occured for the mechanic, and so the diagnostic is not helpful for a specific diagnosis. This is my parents van, and I am very concerned about them being left stranded, as my dad is a paraplegic and cant take a look at it himself. If you have any knowledge on this, please let me know. Thanks so much.
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