Misfire on startup (only on cold days)

Just picked up a 2000 RS this summer. It has been running great so far. I live in Montana and recently the temps have been dipping into the single digits and the car has thrown a check engine light a few times for random misfire and cat inneficiency. But only on the really cold morning a. If it's 20 or above I never have a problem.

Any ideas?:beer: