2001 Tracker starts runs rough, dies and then runs perfectly after sitting for 7 days

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Hi,
I have a 2001 Chevy Tracker, 2.0L engine (105K miles).
Run's well, unless I let it sit for a week or more, then it starts, runs rough and dies.
The fix is easy enough, wait a few seconds, restart and it runs perfectly.
Chevy Dealer isn't sure why..

I like my little Tracker, it was purchased new and has been maintained by the dealer. The only problem I every had was a bad cam shaft sensor that left me stranded a couple of times.

Thanks,
Dan