Replaced O2 sensor now idle too high

*spark plugs not smart plugs.....duh.

Check for a disconnected or cracked vacuum hose. Usually a high idle is caused by a vacuum leak. One of the vacuum hoses may have gotten bumped or moved when you were replacing the spark plugs and you just didn't notice it. The hoses become stiff and brittle over time and on a 16 year old vehicle it's a real possibility. Hope that helps! Jim

Recheck your work, as stated above you may have cracked a vacuum line.