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Is this throttle body supposed to do this?

Discussion in '3rd Gen 4Runners (1996-2002)' started by DLO_Houston, Oct 1, 2024.

  1. Oct 1, 2024 at 12:39 PM
    #1
    DLO_Houston

    DLO_Houston [OP] New Member

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    So some history, my 2001 4Runner had a problem starting (it cranked no problem), and I saw a MAF code, so immediately thought that was it. I replaced it with one from Oreilly's, I forget what brand but I know it wasn't Denso (more on that later).

    Well that got it to start now, but it wouldn't idle, any RPM below 1000 and it would sputter and die. So I bit the bullet and replaced the entire throttle body with a new Aisan throttle body.

    Now it starts and it idles, but is giving me a Bank 1 Too Lean code P0171. So I did a smoke test to find any vacuum leaks. The ONLY place I saw substantial smoke from this test is coming from the throttle body itself where the Accelerator Pedal Position Sensor is. I removed the throttle body to take a closer look and there is an opening on the bottom side, that's where the smoke is coming from.

    My question is, is this normal? I'm leaning towards not normal but I don't know for sure.

    I can't find any other vacuum leaks that would make my engine run lean, other than the throttle body, but if it's not supposed to leak in this spot, I think I can return it as defective. My other suspicion is since the MAF isn't Denso, it is O'Reilly part #MF4226N, Blue Streak Electronics MAF Sensor, that it isn't properly calibrated? One of these two has to be causing my "too lean" code, unless someone can think of anything else. I'm initially ruling out an injector issue as I think that would cause a cylinder specific code like a misfire.

    I went ahead and ordered a Denso MAF, they're only $85 from RockAuto.com, so figured might as well eliminate that variable. Should arrive in a couple days.

    Anyway, here are some photos to show where the smoke test identified the leak on the throttle body.

    Thoughts?

    tb01.jpg
    tb02.jpg
    tb03.jpg
     
  2. Oct 1, 2024 at 2:11 PM
    #2
    AuSeeker

    AuSeeker Old As Dirt

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    Does the old throttle body have that same hole?

    If so put it back on and see if the smoke still comes out there, I know of no other way to see if the new one is defective other than that.
     
    DLO_Houston[OP] likes this.
  3. Oct 1, 2024 at 2:14 PM
    #3
    Dillusion

    Dillusion Resident A**h***

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    Pull the maf and look for an o ring.

    Might be missing or pinched.
     
  4. Oct 1, 2024 at 7:10 PM
    #4
    negusm

    negusm New Member

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    How much was this TB? Is it new? It looks rebuilt. I'd return it and get a full brand new one straight from TOYOTA. TOYOTA's prices dropped on these and I think they were like $450 last time I checked from McGeorge (now Ourisman).

    Regardless, I agree with you, you can't have smoke coming out of that or you have unmetered air. So compare the old one. Put the old one on and see.
     
  5. Oct 3, 2024 at 11:34 AM
    #5
    DLO_Houston

    DLO_Houston [OP] New Member

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    Turns out, looks like I tossed the old part already, but in lieu of putting the old TB back in, I just covered up the (weep?) hole in the new TB with some foam tape (double sided tape where I left the cover on one side), and saw no difference in my AFR and FT readings.

    And my new Denso MAF arrived today, so seeing as I have NO vacuum leaks but the PCM still thinks it's running lean, I quickly swapped in the new Denso MAF.

    WUT!?!?!?! Seriously, the change in the readings was instantaneous!!! So I'll admit it, I was skeptical before that electronic parts like this need to be OEM, but ya, this made a believer out of me. ALL of my AFR and FT readings are now back to looking like normal operation, the motor runs smoother, and it idles perfectly.

    So I'm sure many here already believe it, but ya, I won't bother with other cheaper third party electronics for my 4Runner from now on, its just not worth the hassle and I didn't really save any money since I had to buy another MAF anyway. Lesson learned (the hard way!)
     
    AuSeeker[QUOTED] and backpacker like this.
  6. Oct 3, 2024 at 11:38 AM
    #6
    negusm

    negusm New Member

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    Awesome!!!!

    A little more advice: NEVER throw old parts away until you've driven a month. It takes that long for codes to show up. You also may forget to move a part from one part to the other.
     
  7. Oct 3, 2024 at 12:44 PM
    #7
    DLO_Houston

    DLO_Houston [OP] New Member

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    Update: Well dang, I thought I had solved the problem, but only partially evidently. When I'm driving, the FT's look normal-ish, my LTs are a little elevated but my ST fuel trims chase zero pretty much. But at idle, I see both the ST and LT FT's shoot way up, and then the MIL comes on again with the P0171 Too Lean code.

    I'm thinking a small vacuum leak in the system still would cause this because the volume of air leaking in relative to the amount of air metered by the MAF - at idle - is larger than when I'm driving and a much larger volume of air is being metered, so the leak isn't as noticeable, and maybe that explains why the LTs are just a little elevated?

    So now I'm back to wondering if my TB is causing this small vacuum leak again? The smoke test didn't show any smoke coming out anywhere else from the intake side. Whew, I thought I had competely solved this issue!

    Here's some scanner screen shots of the Fuel Trims to show what I'm seeing. The left one is while driving, the right one is while idling:

    FTs driving.png FTs idling.png
     
  8. Oct 3, 2024 at 1:30 PM
    #8
    negusm

    negusm New Member

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    One trick is to do the brake cleaner spray trick. Or use most any flammable spray. Spray around the engine\TB while idling and listen for changes in the idle. If there is a vaccum leak, it often pinpoints it.
     
    Toy4X4 likes this.

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