Hi- Car ran 100% until yesterday. Started it after cold (40F) and very rainy day and it revved up really high and stayed there never stalled. I let it idle for a few minutes and shut it down. Restarted a few hrs later and the Check Engine light then was on. Drove home w/ no problems then read code 1-1-3. Cleared code and drove it to work and back home today (50 m roundtrip). CheckEng light didn't return today but it's not 100%. Still revs too high at start. Then sometimes at idle, it will rev high, slowly drop down to below normal (but not stall), then high again, very slowly, w/ no pattern. If bad O2 sensor, would it necessarily cause a 2nd code (specific to sensor)? What's the simplest way to test O2 sensor? What are most likely 2 or 3 causes? (Car has 200k w/ original O2 sensor but don't let that bias you!)