98 blazer wont start when cold

buddy has a 98 with a 4.3
when the temp out side drops below freezing it wont start
he took it to the dealer ship and they pulled it in the garage
so they could check it out
by the time they got around to work on it it had warmed up
enough to start
they said they couldnt find a thing wrong no codes or any thing
any ideas what might be wrong ???