It isn't an O2 sensor causing the idle problem. They don't work that way. However, your CEL codes might still point to them as they now have over 75K miles on them.
More likely guesses for the idle problem would be on the intake air side. The possible culprits there include the ISC, the TPS, the MAF, or the ACT or an intermittent vacuum leak.
You can purchase your own OBDII scanner for under $150. Also available is an interface and software package from Alex Pieper for around $120 (less if there is a group buy).
Guess all you want to, but without the CEL codes, you might as well head for the casino.
Steve
PS. It also helps tremendously if you specify your year, engine and transmission.
