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Car stumbles after A/F sensor replacement

Discussion in '1st Gen. Tacomas (1995-2004)' started by jwetering, Oct 5, 2019.

  1. Oct 5, 2019 at 11:12 AM
    #1
    jwetering

    jwetering [OP] Member

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    Hi guys.

    2001 Tacoma 3.4 v6 auto Prerunner 156,000 miles - I've had it for 6 months now. Good clean truck.

    1) About 5 months ago the truck started to stumble at light throttle, but only sometimes. Felt electrical so I replaced the spark plugs with correct dual electrode. Problem went away for the summer.

    2) About two months ago I started to get the P0171 lean bank 1 code and fuel trims were hitting 20% and even 30% but the truck ran actually fine. MAF was visibly dirty so I cleaned it and the code went away and fuel trims fell right into line +/- 5%. That took me longer than it should have to figure out (I'm busy) which brings me to about two weeks ago.

    3) Not a week after I cleaned the MAF the CEL came back on and I got a P1133 A/F heater error code. I replaced the MAF thinking that A/F was the MAF but when the code didn't clear I googled it (duh) and figured out that the MAF and the A/F sensor are different things entirely.

    I verified that the heater on the upstream O2 sensor (which is the A/F sensor for those who don't want to make the same mistake I did) was actually bad by measuring lack of continuity between the two black wires on the sensor. I ordered and installed a new Denso 234-9001 from Rock Auto, cleared the code and took a short test drive. Everything seemed ok, CEL stayed off.

    The next morning though, and right out of my driveway while the engine was still cold, the truck started stumbling at light throttle like it did when I first got it six months ago. The problem is consistent every time I start off from cold and the stumbling only goes away when the engine gets fully up to temp. Even then it feels like it's low on power a bit (very subtle).

    This morning I unplugged the sensor and set out on my normal morning commute and the problem was *not* there. I stopped at a gas station and plugged the sensor back in and the motor felt weak but did not stumble because I suspect by then there was enough heat in the system by then.


    So - what do you guys think ?
     
    Last edited: Oct 5, 2019
  2. Oct 5, 2019 at 11:16 AM
    #2
    eon_blue

    eon_blue 8" third member

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    Which brand sensor did you buy? Denso is the OEM sensor brand for these trucks, any other brand is a crap shoot as far as whether it will work well or not.

    Also beware of cheap prices on 'Denso' sensors on ebay and Amazon...lot of fakes on those sites
     
  3. Oct 5, 2019 at 11:19 AM
    #3
    jwetering

    jwetering [OP] Member

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    Yes - my first thought also.

    Per the thread above - "I ordered and installed a Denso 234-9001 from Rock Auto." Whether or not it's a cheap knock off or whether Denso isn't as good as we think they are is a really good question.
     
  4. Oct 5, 2019 at 11:22 AM
    #4
    eon_blue

    eon_blue 8" third member

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    If its from Rock Auto then you should be good as far as it being legit, they are a reputable online source for parts.

    Toyota builds these trucks around the exact parameters of Denso sensor specs which is why they can be fussy with other aftermarket brands. But it sounds like you got the right one in there. I guess my other question would be, is the seal around the sensor good? If there's a leak around the gasket it might throw off it's readings and cause some weird behaviour
     
  5. Oct 5, 2019 at 11:39 AM
    #5
    Area51Runner

    Area51Runner Well-Known Member

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    234-9001 is the correct one for your truck (I have the same sensor).

    Only thing I can think of is possibly defective? Not sure what they charged you but it should've been about 125 bones. If substantially cheaper, I'd question it.

    Since the issue went away when you disconnected it, definitely the sensor.
     
  6. Oct 5, 2019 at 11:51 AM
    #6
    cruiserguy

    cruiserguy Well-Known Member

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    Just to make sure I understood, the last trip you describe, before starting the truck you unplugged the AF sensor and then started and drove it (how many miles?, was the engine at operating temp by then?) and it felt normal. - Did the MIL turn on with that sensor unplugged? It should have, I'd think. And when that MIL is thrown the ECU runs in safe mode(for many of the DTCs at least) and richens the air/fuel mix as it's safer to be rich fuel over being lean on air/fuel mix.
    Battery was unplugged while you swapped the sensor right? With new sensors the ecu remaps the fuel and air values, yada yada or something like that
     
  7. Oct 5, 2019 at 12:13 PM
    #7
    jwetering

    jwetering [OP] Member

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    1) I did not unhook the battery when I unplugged the sensor but the ignition was off.

    2) I started the car after I unplugged the sensor and drove about five miles.

    3) The MIL (I call it the CEL) came on yes and gave the same P1133 A/F heater error code.

    4) I paid $163 CDN which works out to about $125 USD - so yeah it sounds like the same one other guys are using successfully.


    So - could it be as simple as disconnecting my battery for a half hour after changing that sensor ? I will try but will be very surprised if it works.

    Anything else gents ? - Consensus so far is that I have a faulty A/F sensor ?
     
    Last edited: Oct 5, 2019
  8. Oct 5, 2019 at 12:43 PM
    #8
    cruiserguy

    cruiserguy Well-Known Member

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    I didn't say I think you have a faulty new sensor but I'm not not saying it lol :DI think replacing it though was the correct move based on your proper troubleshooting of the continuity of the heater circuit wires.
    If your MIL isn't on but you're experiencing that same stalling type issue with the new sensor, as in it runs the same as before you swapped the sensor, than it sounds like there is something else going on. But the new sensor addressed that heater circuit issue. Am I understanding your scenario correctly?
     
  9. Oct 5, 2019 at 12:44 PM
    #9
    cruiserguy

    cruiserguy Well-Known Member

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    But yes you gotta get that fuel map re learned or plotted or the old one erased. Whatever it is that it technically does when you disconnect the battery for a bit
     
  10. Oct 5, 2019 at 12:54 PM
    #10
    jwetering

    jwetering [OP] Member

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    Yes - the new sensor addressed the heater circuit issue. The MIL (CEL) went out and I'm showing no codes...I am really hesitant to buy another O2 sensor as you can appreciate. If I did I would go for a Toyota part which means I would be spending some serious $ to try to fix a long shot. I hope I don't come to regret that decision.

    Currently have battery cable unhooked. About to reconnect and see if this helped. It's been about a half hour - I don't accept that this process (if it works) should take overnight as some other threads on the internet have said.

    I will report back.
     
  11. Oct 5, 2019 at 1:37 PM
    #11
    Area51Runner

    Area51Runner Well-Known Member

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    1997tacomav6 and cruiserguy like this.
  12. Oct 5, 2019 at 1:39 PM
    #12
    Area51Runner

    Area51Runner Well-Known Member

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    Give it a day or so. Ideally, it should clear on its own and once the Drive Cycles are complete all should be running good.
     
  13. Oct 5, 2019 at 2:18 PM
    #13
    jwetering

    jwetering [OP] Member

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    Well colour me surprised.

    Hooked the battery back up and went and ran an errand. Truck ran great and furthermore the longterm fuel trim is now running a dead steady 0.0% where it had previously been wavering around negative 4%.

    Resetting the ecu seems to have been exactly what I needed to do.

    I will know for sure tomorrow morning (or tonight) after the engine has cooled completely but I am now feeling good.

    I will report back.

    And yes I installed the gasket that was included.
     
  14. Oct 5, 2019 at 8:36 PM
    #14
    cruiserguy

    cruiserguy Well-Known Member

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    Awesome my man, glad to hear it
     
  15. Oct 6, 2019 at 10:16 AM
    #15
    jwetering

    jwetering [OP] Member

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    OK. Closing the loop.

    Took the truck out this morning, it ran good with only the slightest hint that maybe the fuel was being trimmed a tiny bit more than it should have been.

    Even then this happened only under a specific circumstance when I back off the throttle and am decelerating anyway. The kind of thing that you probably wouldn't notice if you weren't trying to notice it.

    Notably I could see the long term fuel trim was dipping into the negative 3% zone when I did this. It went right back to 0% when I feathered the throttle, and then stayed at 0% during normal part throttle operation. Previously the long term fuel trim stayed at negative 4% even after I started opening the throttle and it seems obvious now that the engine wasn't getting enough fuel at the time.

    Anyway, I call it problem solved. Cruiser Guy gets an internet point for identifying my problem. Saved me from buying new wires and coil packs which is what I was going to do before I posted.

    Thanks bruh.
     
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  16. Oct 6, 2019 at 10:19 AM
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    cruiserguy

    cruiserguy Well-Known Member

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    Seriously was glad to hear it because I could tell from your posts that you're the type that's on top of things, you know? Knowing that and that you used a Denso part I kinda went where we went with it. We all try to pay it forward as we've all been helped as well, you know, that weird universal balance and karma and shiz :D
     
  17. Oct 17, 2019 at 9:26 AM
    #17
    jwetering

    jwetering [OP] Member

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    OK gents - another update.

    A day or two after the A/F sensor issue was resolved the truck set to bucking hard at light/steady throttle . Only sometimes though, and not during acceleration. It sure did feel like an ignition miss but I was getting no code and no CEL.

    That's when it hit me. I busted out the bluetooth OBDII dongle and trended throttle position while one a dead flat road at 60 mph using cruise control.

    I'm using a BlueDriver OBDII scanning tool. Cost me $100 CDN and runs off an app on my phone. Lets me trend all sorts of stuff and of course reads and clears error codes. https://www.bluedriver.com/products/bluedriver-scan-tool

    There are other similar tools on the market but this thing has been a lifesaver for me.

    Sure enough I could very clearly see the indicated throttle position dropping out during steady state operation at the same time that the car stuttered. This problem went almost entirely away when the car was driven for a long time (like 30 minutes or more) and was worst right out of the driveway in the morning.

    I ordered a new throttle position sensor (TPS) that night at dinner from Rock Auto. I bought the Beck Arnley part for $50 plus $16 shipping to Canada in four or five days. There was no Denso part listed.

    Over the 4 days or so it took for the part to arrive I gathered more data and interestingly the problem disappeared (almost) entirely in the last couple of days. Intermittent problems are the worst.

    I installed the part last night and the test drive went very well and this morning it ran really well also. I think I finally beat it - but hey I've been fooled before.

    So in recap for guys that are troubleshooting similar problems in the future:

    1) Car stumbled at light/steady throttle - replaced spark plugs with proper dual electrode - problem seemed to go away away.

    2) Months later I got a Check Engine Light (CEL) and "lean condition bank 1" code but ok operation - cleaned and then replaced the Mass Air Flow sensor (MAF) - light went out and code went away. Car ran ok. I actually replaced the fuel pump during this time also thinking that was the problem. It wasn't, but now I have a new fuel pump which is good.

    3) Soon after that I got another CEL and "A/F sensor heater bad code" - verified bad upstream O2 sensor heater and replaced. Code and light went away but car ran poorly. Disconnected battery to reset ECU and car ran better - verified long and short term fuel trims fuel trims were reset to 0% each.

    4) Soon after that the car started stumbling again at light/steady throttle but problem went away after driving for a while- no CEL and no codes - trended throttle position and verified was dropping out intermittently. Replaced Throttle Position Sensor (TPS) and car runs great.

    I bought the truck off of a guy that had it parked for the last year he owned it. I think he started seeing some trouble and didn't have the time/resources/understanding to fix the issues. Seems like it was just time for all of those sensors to fail and maybe the long term park-up played a role as well.

    Despite all of this I've never stopped liking the truck and it never really let me down. I think I spent $200 in total (plus $100 for the fuel pump) so no big deal.
    I really do think I have it sorted now. Fingers crossed.
     
    Last edited: Oct 17, 2019
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  18. Oct 17, 2019 at 10:09 AM
    #18
    cruiserguy

    cruiserguy Well-Known Member

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    Awesome man and great to hear. I appreciate all the data points you kept track of. Will definitely help folks in the future. Good on ya:D
     
  19. Oct 18, 2019 at 7:36 AM
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    Glamisman

    Glamisman Well-Known Member

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    BlueDriver... imho the best inexpensive scan tool. Plug it in connect to the iDevice, set your logging parameters and drive. No cables No hassle. If deeper digging is required hook up Snap On.
     

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