O2 sensor keeps going bad and rpm bouncing.?

tell him to check the wire from the 02 sensor ! when it,s running the 02 sensor is suppose to get full voltage all the time ! it could be like a car i had once ! the trouble with it was the battery terminals were all corroded and stopped the voltage from getting to the sensor ! after i cleaned them up good then the check engine light stayed off !

Didn't do a good enough job on the IAC and THROTTLE BODY! They should be removed and cleaned to hospital floor clean. If idle is jumpy, this is usually why. It is a LOOP! When the IAC is dirty, fuel/air mixture will also be off. The O@ sensors get clogged with carbon, and this sends a signal to the IAC to add or subtract incoming air. Until the IAC is perfect, the O2 sensor will go nuts. DO a full motor sludge removal treatment, as the cam adjusters are vulnerable to sludge. Use ONLY synthetic oil, 0w-30 Mobil ONe in there. THese engines can blow the expensive exhaust manifold when the fuel mixture is bad. VERY EXPENSIVE INDEED More than $500. WHen you are SURE that the IAC and t body and EGR and PCV valve are perfectly cleaned up, install a fresh set of DENSO IRIDIUM or BOSCH IRIDIUM spark plugs. GOOD LUCK! This will insure best power and economy. Those engines are EXCELLENT and will last longer than the car will. Install a new genuine BOSCH O2 sensor, they are the best on the planet. The CEL light is practically telling you that the IAC is still filthy inside. AMSOIL FOAMING CLEANER and GUMOUT will remove all the contaminants, and restore air/fuel mixture. GOOD LUCK!

Just a guess but I'm thinking with the lose of power and the O2 being just after a tune up the mechanic got the plug wires crossed. If it wasn't running that bad when you took it what do you think? Maybe Pepboys is not the best place to go.

With your RPM fluctuating up and down, you likely have a vacuum leak. Check all your vacuum hoses for worns hoses. A vacuum leak will cause fluctuating RPM and your gas mileage will drop dramatically.