A few comments:
Possible engine control module, we have seen a few with complaints similar to this one, where the mixture is driven too lean on cold start-ups. Any check engine light as a result of the poor performance?
Engine coolant temp sensor, but it would be rare.
Mass air flow sensor, but again it should set a code and check engine light.
Going to have to get the computer checked for codes, and if nothing there, maybe leave it a few days so they can get it to happen and hopefully discover the cause. if the check engine light is coming on, shouldn't be too hard to nail down a cause.
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