For those searching on this problem as I did...
Cold starting was hard; didn't even have to be that cold. Backfiring and poor drivability until warm, then OK.
No check engine light.
Based on previous suggestions, I replaced the coolant temperature sensor. That completely fixed it. Good thing, too, I'm not sure what I would have tried next.
BTW, getting to the thing is a b*tch. I once did it on my '95 impreza and couldn't remember just how. This article was most helpful! Step by step photos.
Those hoses didn't just slip off, however!
Bill Hale Loveland CO