2000 Expedition O2 sensor errors/rough idle
I have a 2000 Expedition (110,000 miles), original owner and about 4 years ago, the check engine light came on. Had it checked out at Tires Plus and they said it was indicating a problem with the O2 sensors, nothing specific. They tested each sensor and they passed. Reset the alarms, light went of but came on the next day. Have not had any engine problems until recently, have had them check test the codes, always indicates O2 sensors, test of these pass each time. This last time the code indicated a specific O2 sensor was bad. I've noticed I'm now having rough idle in cold weather, it gets better once it warms up. I've had a tune up done, new plugs a year ago so my question is, can a bad/failing O2 sensor cause this behavior or is there something else I should be looking for?