i was reading something and it said when u do ur tune up u should change ur o2 sensor also. is that necessary? i never changed it from i had the car (3yrs). i noticed lately that my car stutters once in a while when accelerating.

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Im not saying thats what the problem is, but they do get lazy over time, so if you know they havent been changed in a while, its not a bad idea to go ahead and put new ones in. If it were me, i would leave the rear one though. its only real purpose is to track the cats efficiency, the front one is the one that actually changes AF ratios. as for the stuttering, have you tried seafoam? my worktruck got such bad hesitation, I couldnt merge into traffic, and I ran some through it, and its ran fine ever since.

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Yes, there's a "Replacement for Displacement". Its called Volumetric Efficiency.

I believe the back o2 sensor is also there to tell the ECU if the front o2 sensor is working properly. I remember hearing that if only your front or back o2 sensor is bad, then your ECU will throw a code.

i think i might try that seafoam thing because i read a lot of good stuff on here.

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Although sea foam is some good stuff when used correctly, I don't think that will help your problem. If your O2's were getting that lazy to the point you feel the car hesitating or chugging, it would set a code immediately. I don't think your O2's need changing, if they did most likely you would have a CEL. I think you may need a basic tune up if your feeling your car stuttering, it's probably cause by a misfire. spark plugs, plug wires, distributor cap & rotor, air filter, fuel filter and PCV valve if you want to do the tune up right. Also gain access the the throttle blade and clean around it with brake clean, a toothbrush works best, you'll notice a dramatic difference in throttle response and idle quality....especially if it's really dirty.
The front O2 is only used in closed loop(always trying to meet 14.7 afr), or below say 20% throttle/give or take. After that your ecu switches over to open loop(preprogramed air fuel ratio's and timing number maps) which does not use the O2.

After that get it tuned if you really want it to run at peak performance!

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There is no replacement for displacement, except for some boost of course....