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bad idle, just changed O2

Discussion in '1st Gen. Tacomas (1995-2004)' started by feebs03, Aug 13, 2012.

  1. Aug 13, 2012 at 4:26 PM
    #1
    feebs03

    feebs03 [OP] Well-Known Member

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    CEL was on, got it read, changed o2 sensor (rear), drove about 60 to 70 miles after the change, CEL light didnt go off. i just disconnected the battery now my truck idles under 500 rpm. what do i do? drive it and hope the computers reset or what?

    thanks
     
  2. Aug 13, 2012 at 4:38 PM
    #2
    Ecnerwal

    Ecnerwal Well-Known Member

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    Did you pull the fuse or battery cable (fuse is less work) when changing the O2 sensor?

    Depending on the particular code, a "rear O2 sensor" code can be a bad sensor, or it can be sign of dying catalyst; at least AFAIK.

    I'd suggest pulling the cable or fuse for an hour or so, and you might clean the MAF while you're waiting (read up on how - don't break the foolish thing) and double-check that the connection to the new sensor is good.
     
  3. Aug 13, 2012 at 4:52 PM
    #3
    feebs03

    feebs03 [OP] Well-Known Member

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    no i did not pull the cable when changing sensors i will go pull it now and leave it for a while
     
  4. Aug 13, 2012 at 5:45 PM
    #4
    Ga tacoguy

    Ga tacoguy Well-Known Member

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    :) Do you remember what P0 Code was given to you, when it was read for you. Most times it is the front O2 sensor that fails, rarely the rear one. I do not think your battery cable removal will fix your problem. Good Luck.
     
  5. Aug 13, 2012 at 5:59 PM
    #5
    feebs03

    feebs03 [OP] Well-Known Member

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    do not remember the code but said bank 2.... is it the same part number? i might just replace it too
     
  6. Aug 13, 2012 at 6:22 PM
    #6
    Ecnerwal

    Ecnerwal Well-Known Member

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    Get it read again (if, in fact the light comes on again and things still run strangely.) The specific code will get you better answers. You have the V6? If not, you don't have a bank 2. If so, you do, but you still might not have a sensor there.

    The 4's have bank 1 sensor 1 (air/fuel, aka "front") and bank 1 sensor 2 (oxygen, aka rear.)

    The 6's actually have Bank 1 ( the 3 cylinders with cylinder #1) and bank 2 (the three other cylinders) but according to the service manual (not an engine I own) they still only have the single front and rear sensors (bank 1 sensor 1 and bank 1 sensor 2) in front of and behind the cats, since the two sides come together before the first sensor. 1 is front, 2 is rear.

    The front sensor is not the same part number, and costs a bit more (or less depending where you bought the rear one and how much they overcharged.) Denso 2349001 for A/T, 2349002 or 2349003 for manual 4 or 6 (sensor same, wires diffferent. Rockauto (look in the vendor section for a 5% TW discount code) seems to be the best price around, at about $100 for the front and $60 for the rear (approximate, and before discount.) If $100 is a big deal to you, don't replace the front one until you get a code for it - if $100 is not a big deal, and you are sure the code you got was for sensor 2 whcih you have replaced, replacing the front one makes sense IMHO. Sensors are cheaper than cats. Wisdom around here is to stick with Denso sensors since Denso makes the original Toyota sensors...
     
  7. Aug 13, 2012 at 7:27 PM
    #7
    tacoma04

    tacoma04 Laissez les bons temps rouler

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    This is correct AFAIK. I have changed the front O2 sensors of my two tacos (both V6 engines) and the exhaust from bank 1 and bank 2 join before the first O2 sensor. So the rear should say bank 1 sensor 2. If I am wrong, someone more knowledgeable will correct me.:D
     
  8. Aug 13, 2012 at 7:43 PM
    #8
    feebs03

    feebs03 [OP] Well-Known Member

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    Okay well the idle is back to normal...(i think...a bit over 500 in gear and right around 750 in park) the light is still on. i do have the v6 3.4 i will take it to a different place tomorrow to get it checked (the first place just wanted to sell me something so he said alot of stuff and i really wasnt listening) air/fuel sounds like something he said but i have the v6 so idk really i will have it checked tomorrow. I did buy the first one from rock auto didnt know about the discount tho... thanks for the input. I just cant stand the check engin light :frusty:
     
  9. Aug 13, 2012 at 8:46 PM
    #9
    Ecnerwal

    Ecnerwal Well-Known Member

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    P1135 is the air/fuel preheater (on a 2.4 or 2.7L - evidently P0031 or P0032 on a 3.7L V6). There are some other codes that indicate issues with that sensor, but that's a common one. It's bank one sensor one - Rock Auto calls it an oxygen sensor (you won't find air/fuel sensor in their emissions parts), but Denso calls it an air/fuel sensor (right on the box RockAuto sent) and so does Toyota and the diagnostics. Similar to each other, but they read differently, or something like that.

    A P0420, on the other hand, indicates that Bank 1 sensor 2 (the rear one you just replaced) is out of range, and if the sensor is good (a new one should be) it means (or may mean...) the cats are bad, which gets expensive. Exhaust leaks and both sensors are before replacing the cats, though, so it may just be needing the first sensor replaced if the second didn't do it.

    The preheater fail does, in my limited experience, cause an instant CEL even if you reset the thing (which, among other things, the battery cable or fuse for an hour should do.) I advise new lockwashers, stainless steel nuts (8x1.25mm) and antiseize (sensor safe, please - don't poison your sensors with silicone) for putting them in to give better odds for getting them out with less swearing next time.

    Pull the fuse or battery cable again if the front sensor is being replaced. While it should reset the light (if the problem is cured) it more importantly resets the computer so that it "learns" the new sensors from it's "default settings", rather than adjusting from where the old/failing or failed sensors had got it adjusted to.

    Cleaning the MAF is pretty simple if you are careful, just takes a can of MAF cleaner or electronic contact cleaner (not cleaner and lubricant, just cleaner) and helps the computer to have a more accurate idea of the amount of air coming into the motor - which helps it get the amount of fuel for a correct mixture right.

    In any case, go find out what codes you have and we'll be able to get to the point of your actual problem, rather than trying to cover all the bases it might be. If you're idling better, that's progress, at least.
     
  10. Aug 13, 2012 at 9:24 PM
    #10
    Robertgeejr1

    Robertgeejr1 Well-Known Member

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    I have done all the hi-pro mods for a life time, since I got this truck at a great price, I will be happy with showroom new.
    i hate to harp on this and the last time a 20 year gave me a response back about thats life, like he has any ideas,
    but after 100,000 miles or more, do you and the truck a favor and replace the sensors in pairs.
    after the cel light is on you are damaging the cats. I have found its best on something like this to try to just leave the battery unhooked over night, and in the morning just hook it back and let it relearn.
    and it is strange for the back sensor to go out first, its sort of the back up, the first one does most of the control.
    after i replaced both, my truck ran alot better.
     
  11. Aug 14, 2012 at 2:23 PM
    #11
    feebs03

    feebs03 [OP] Well-Known Member

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  12. Aug 14, 2012 at 2:30 PM
    #12
    Ecnerwal

    Ecnerwal Well-Known Member

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    Yes. don't forget to use the TW discount code and save yourself almost $5.

    TW rockauto discount should be in here:

    Also go out and spray down the nuts (or what's left of the nuts) on the front sensor with your penetrant of choice - Kroil, PB Blaster, Liquid Wrench, some other brand name, 50/50 ATF+acetone (the homebrew stuff) every time you get home (so it's nice and hot-ish, but not so hot it catches on fire) from now until the part arrives. Improves your odds of getting them (or what's left of them) off.

    If you don't get mislead by the video (read the posts after it) this is the best I can find (not great) for MAF cleaning, which I would suggest doing along with the front sensor replacement. I didn't watch the whole video, but don't do anything crazy like taking out your whole intake as they did - should be just a couple of screws and one wire harness connector - spray the thing with cleaner (don't touch the wires, don't poke anything at them, etc. MAFs are expensive) let it dry and reinstall - 5 minutes or less.

    http://www.tacomaworld.com/forum/performance-tuning/127178-mass-air-flow-sensor-cleaniing-question.html
     
  13. Aug 15, 2012 at 9:28 AM
    #13
    RacerP

    RacerP Well-Known Member

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    And after you replace it, don't be surprised if it runs like a crap...low idle.

    Mine did exactly the same thing, and it takes a few miles for the computer to sort itself out. Don't ask me why.

    If it turns out to be your cats, Magnaflow has pretty good universal cat, have had it in my truck for about 5 years now without it throwing a CEL
     

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