Engine Performance problem
2003 Ford Taurus 6 cyl Front Wheel Drive Automatic 150036 miles
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The check engine light came on about a week ago and the car began running rough at very low speeds and when idling. Autozone's OBD II diagnostic computer spit out O2 sensor codes. I replaced both the O2 sensors but the car runs just as poorly as before. When the RPMs are below 1000 it bucks and even quits if you sit still in traffic for more than a few seconds. Do I need to replace the rear O2 sensors or is this a Mass Air Flow sensor problem or something else? I don't want to spend more money on a guess and check fix.

well I wanna say your idle air control valve by what your telling me, but here are a couple of things that you can check on your own that will put checks next to the list of possible causes. one is ignition and spark and the other is fuel pressure. I will send you a couple of video links that will show you the easy way to do these your self. hang tight.

her is a link to show you an easy way to check ignition and spark.:


http://www.2carpros.com/car_repair_video/test_engine_ignition_system.htm

HERE IS A LINK TO SHOW YOU AN EASY WAY TO CHECK FUEL PRESSURE/l . Also remember to check for vacuum leaks first before anything else

http://www.2carpros.com/car_repair_video/test_fuel_injection_pressure.htm

If it were either of those things, wouldn't I expect performance problems all the time, not just when the car is in idle?

not all codes related to o2 sensor means that sensor bad
if you have the p code that auto zone came out with
that p code will help to pin point the trouble area
check for a vacuum leaks and check mass air flow sensor
check egr valve (if have one )

If you're getting codes showing multiple o2 sensors faulting, most likely it's something other then bad o2 sensors, usually multiple failures are uncommon. Check for a vacuum leak somewhere, check the pcv hoses for pinholes, a common cause of lean codes,, as an aside, my son's 93 Taurus spit out o2 codes, indicating a lean condition, turns out the ground was corroded.


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It was a vacuum hose leak.

Thanks for the help all.