I have a rough idle on my 1993 4x4 with the 22re in it. It has about 125000 miles. I have had the o2 sensor code come up before but had it looked at and my mechanic said it seemed to be working fine. Can a bad O2 sensor cause a rough idle once truck has been warmed up?

Also where is the cheapest place to get a "factory" sensor from?
Thanks for any help