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IAC-No Input Voltage / HIGH TRANS TEMP

Discussion in '1st Gen. Tacomas (1995-2004)' started by j4roe, May 28, 2020.

  1. May 28, 2020 at 10:16 AM
    #1
    j4roe

    j4roe [OP] Well-Known Member

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    Good afternoon to the fine folks of TacoWorld. I have run into a few issues with my truck over the last few months. I have detailed and documented my problems in my truck's build thread in the LT section. I didn't want to start cluttering the forum with threads in different sections but I realize that I'm pry not getting all the exposure I need for these MECHANICAL questions in the SUSPENSION section LOL. With that being said, I will post the link below to my build page in order to read the background of these issues and what I have done to diagnose the problem.

    Pages 7 or 8 through 10 are going to be related to the IAC high idle issue and the high trans temp.

    https://www.tacomaworld.com/threads/el-honcho-1st-gen-taco-build.646535/page-10#post-23455407

    Both problems arose after this Doug Thorley header install. IAC is brand new and was bench tested. Resistance is in spec. Applied 12v respectively on the bench to the two other posts on the IAC and the motor moves the direction it's supposed to each time. Put the truck back together and have had an incredibly high idle ever since for the last month or so. With truck at operating temp, again the IAC resistance is in spec, 23 and 24 respectively. Key in, engine running I have battery 13.5v on the middle pin however, the two end pins I only have .02 and .02. So basically when you plug the IAC in the motor shoots up to 1700 as high as 1900. I have confirmed NO VACUUM LEAK. Obviously because the RSC RSO pins aren't getting voltage the IAC is being held WIDE OPEN! FSM says, no voltage on these pins check ECU/WIRING. The wiring looks fine and it goes straight into a loom that goes straight back through the firewall into the ECU area behind glove box. I can't understand how there could possibly be anything different in the 3 weeks the truck was sitting for the header job. I'm basically at a loss for what to do next now that I know I'm not getting the correct voltage on those two pins of the IAC connector....

    Second problem, ever since the new headers installed the trans temp is now getting high. Just normal driving for 15, 20 minutes in the city and the trans is getting up 250, 260. I've been running a OBD2 device for a year or so now so I know exactly the range my trans used to heat up to in given situations. I've never seen this thing above 217 in the city or NOT towing anything. The trans is shifting excellent as it always has in the 12 years I've owned it. No slipping, no hard shifts. Fluid is at the correct level. Pry on the dirty side but nothing atrocious. It's almost as if the radiator is not heat exchanging the trans fluid or the trans fluid itself isn't circulating as it should... I'm absolutely stumped at this point.

    Thanks amigos!

    Joe
     
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  2. May 30, 2020 at 9:44 AM
    #2
    j4roe

    j4roe [OP] Well-Known Member

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    BUMP up the volume
     
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  3. May 30, 2020 at 9:52 AM
    #3
    Black DOG Lila

    Black DOG Lila Well-Known Member

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    Stock. EZ pass.Dump pass.Inspection sticker.Convict printed lic.plates.FG cap.
    Headers get a LOT hotter than stock cast iron exhaust manifolds

    Check inside throttle body for scouring and fitment of butterfly.
     
  4. May 30, 2020 at 10:42 AM
    #4
    Ccrowe323

    Ccrowe323 Well-Known Member

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    Man you should change that trans fluid right away, really anything over 210 starts to degrade the fluid quite a bit. Especially up into 270 that’s really high and could possibly damage the trans. @gearcruncher is the guy to talk to about transmissions. Check out his write up on the a340 trans
    https://www.tacomaworld.com/threads...sions-write-up-your-4-speed-automatic.325531/
     
  5. May 30, 2020 at 10:50 AM
    #5
    Ccrowe323

    Ccrowe323 Well-Known Member

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    Is that an Eric B. & Rakim reference or am I reading to deep into it? :rofl:
     
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  6. May 30, 2020 at 6:27 PM
    #6
    j4roe

    j4roe [OP] Well-Known Member

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    LOL YEP!
     
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  7. May 30, 2020 at 6:29 PM
    #7
    j4roe

    j4roe [OP] Well-Known Member

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    I will read that thread IMMEDIATELY! I swear to god this has to be a circulation issue... There's heat transfer in P after it gets high. It will slowly fall in P. In D on the freeway or extended road with no stop lights 50-70mph has little to no heat transfer which is weird. I agree with changing the fluid. I just bought a filter. It's NEVER been replaced in the 12 years I've owned the truck. Sad to admit.
     
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  8. May 30, 2020 at 7:17 PM
    #8
    Ccrowe323

    Ccrowe323 Well-Known Member

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    Hmm that is weird. Usually highway generates the least amount of heat.
    Check out this thread post #10, gearcruncher list a couple really good links, especially about trans coolers. https://www.tacomaworld.com/threads/4runner-tacoma-a340f-compatibility.630349/

    Just wanna say I’m no expert, I’m just giving my 2 cents on how I’d take care of my truck.

    Before I decided on doing the manual swap (trans is slipping due to pink milkshake) I bought this trans cooler after doing some researching and hearing it’s the best.
    https://www.amazon.com/gp/aw/d/B005XZXB1M?psc=1&ref=ppx_pop_mob_b_asin_title
    I never installed it and returned it after decided to go manual, wish I could help ya with the install but I believe the T’Cha @Timmah! has a video on it.
    Ive always heard people say never change your trans fluid. But I have recently learned that it’s kinda just a myth.
    Yes changing trans fluid can harm your trans if it’s done incorrectly such as flushing it in its opposite flow. I think it would be better just to do frequent changes so it stays clean, rather than flushing. Probably like every 25-30k miles, or if it overheats, to me would be 212 and above, or change it sooner if you tow or wheel hard.
    Also check your pan magnets and see how much accumulation is on them, or any larger bits
    I personally have changed mine before in a 98 S/C 4runner with 300k miles, I didn’t drop the pan or change the filter, I just cHanged the fluid. Drove it for about a year and a half, maybe 15k miles, and still shifted just as smooth when I sold it.
     
  9. May 30, 2020 at 9:56 PM
    #9
    Timmah!

    Timmah! Well-Known Member

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    I wouldn't consider a trans temp of 212 degrees a benchmark for a fluid change. The life of the fluid does depend on the temperatures it's been heated to but it also depends on mileage. If your trans temp never exceeded 170 degrees, it could last you 100,000 miles. But, auto transmissions can easily go over this mark any time you drive in the mountains. The higher you raise the temp of the fluid, the less life it has. When I'm driving in the mountains or 4wheeling, 230 degrees is a benchmark I use to let me know it's time to pull over and give my transmission and engine a rest to cool down. But, it doesn't mean when I get home I do a fluid change. Now, If I really overheated my trans and got it close to where the idiot light comes on at 300 degrees, I would do a full flush when I got home.

    To keep my fluid in good shape, I do a drain and refill of the pan every 10k miles. I like introducing fresh fluid more often due to the fact my transmission is being pushed harder from driving quite a bit in the mountains.
     
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  10. May 30, 2020 at 10:27 PM
    #10
    j4roe

    j4roe [OP] Well-Known Member

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    My concern lies more with the behavior of the temperature. I've had the OBD2 Torque Pro for about a year and a half. I have a really good idea what the temperature has been in certain situations. It takes 15 or so minutes for it to get up to 200 but then its 215 and then 225 and then 242... Today on a 37 minute "test drive" to get a smoothie I hit 267... It was 112 today but I've owned this truck 12 years no tranny issues whatsoever, 1.25-1.5 years with Torque pro... I put it on the freeway for 10 minutes sustained airflow at 71mph and the temp just really didn't drop like I would normally see. For the last year and half at least owning this Torque Pro I've been towing the jet ski to Mexico, 3.5 hours one way and the temp would get to 240 constantly downshifting into a headwind at 3k... which would be the expected outcome. Basically the scenario I'm experiencing right now has an ADVERSE relationship. Easy driving and the temp keeps climbing past the 20 minute mark of driving... Normally what I see is a more direct relationship between variables in engine load, heat, rpm, shifting, sitting in traffic... So certain scenarios have a more predictable outcome and right now 20 minutes of light city driving should not be heating the trans up to 267 and from what I've seen the only way this goes down a little is stopping and putting it in park. No chance. Absolutely zero chance there isn't something "wrong". I was starting to research the solenoids because one of the three must be the pickup from the strainer... I really feel like this is a circulation/heat exchange issue. The trans operates very well and always has. The temp is too high and I don't want to keep driving it without knowing if this is false reading or circulation/heat exchange issue. Only variable since high trans temp is the DOUG THORLEY HEADERS!!! Damn... I've had some bad beats lately. LOLOLOLLLLLLLLLLLLLLLLLLLLL

    I've had like 5 Tecate ROJO "CON MAS SABOR" watching LA self destruct.
     
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  11. May 31, 2020 at 12:28 AM
    #11
    NvrSyNvr

    NvrSyNvr Well-Known Member

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    Any chance a grounding strap was removed or missed during the header install? If you have not already, I might consider doing ground tests at various locations around the engine bay. Also.. I was getting trans temps like you describe a few years ago. If I remember correctly, I could smell the burnt fluid of the trans at those temps. Also, when hot, I would start to get unusual behavior from the trans. I wonder if you could verify the temperature using an infrared thermometer if you have access to one?
     
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  12. May 31, 2020 at 5:08 AM
    #12
    Ccrowe323

    Ccrowe323 Well-Known Member

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    That’s true, maybe 212 is pretty low to require a change haha, I was meaning more if it’s already got 15-20k miles and it gets higher just change it early but yes 10k is even better. Thanks for adding in, def better info than I provided haha:cheers:
     
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  13. May 31, 2020 at 7:31 AM
    #13
    Glamisman

    Glamisman Well-Known Member

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    I have always held the opinion that chaning fluids early and often is cheap insurance. If you do the work yourself it isnt too expensive to dump what, 7 quarts of ATF... $35 at $5 a quart.
     
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  14. May 31, 2020 at 9:30 PM
    #14
    Digiratus

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    OP, are you running an external fluid cooler? I haven't seen it mentioned if you are.

    FWIW, I installed the Thorley headers a few months ago. I monitor my trans fluid temps with a scangauge and have not seen any temp behavior change compared to before the swap.

    I am running a Tru Cool trans cooler in series with the radiator. Since adding the cooler several years ago, even under the harshest conditions, (steep grades, really hot days) I never see 230° any more.
     
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  15. May 31, 2020 at 9:35 PM
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    5amStevens

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    Add a transmission cooler.
    I'm in AZ as well and it dropped my temps about 30 degrees.
    Here's a not so great pic.
    IMG_20200331_170458_0.jpg
     
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  16. May 31, 2020 at 10:51 PM
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    gearcruncher

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    A computer controlled torque converter needs proper input from the IAC circuit .
    Is your torque converter locking and unlocking as it should ? This would create all that extra heat you are trying to figure out . That converter clutch needs to be locked at freeway speeds
     
    Last edited: May 31, 2020
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  17. Jun 1, 2020 at 5:51 AM
    #17
    nzbrock

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    I was about to say the same thing gearcruncher did. When you're cruising on the highway in your highest gear at a set speed, the torque converter will lock up. This will cause your fluid temp to drop since the transmission is now directly "connected" to the drive train and not "slipping" anymore.

    What about your throttle position sensor? I would go over every single wiring connector that needs to be removed in order to install the headers. Use the FSM and go step by step. I bet there is something disconnected, or something got damaged in the process.
     
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  18. Jun 1, 2020 at 11:33 AM
    #18
    j4roe

    j4roe [OP] Well-Known Member

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    Only ground that was removed was from upper plenum, driver side right under the diagnostic box. It was reinstalled.
     
  19. Jun 1, 2020 at 11:36 AM
    #19
    j4roe

    j4roe [OP] Well-Known Member

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    No cooler but I definitely plan on it. My concern stems from monitoring the trans temp for the last year or so and having an understanding of the relationship between the torque converter and the trans temp. The temp has been consistently 20 or 30 degrees higher the last month or two since I put everything back together from the header install.
     
  20. Jun 1, 2020 at 11:56 AM
    #20
    j4roe

    j4roe [OP] Well-Known Member

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    This is exactly what my theory was. The IAC is stuck wide open so the crank is spinning 1900 in P and when you put it in drive, the torque converter is locking up (stall speed) and trying to push through the brakes. So when you're sitting there in D with the brakes pressed it's idling at 1150, 1200... to me understanding relationships, this would create more heat. I have also noticed a direct relationship between the temp and being motionless in D. Temp goes up. Waaaay up. Never seen it go up this high or like this. Been in many In n Out lines in the middle of July, 20 minutes with no air going to the radiator and NEVER seen 250 sitting in place. Yesterday, took the truck to the Anthem outlet mall. 20 mile drive. Mostly all freeway. If I kept the truck in OD at 2200, 71mph 217 degrees. As soon as the cruise control needs to downshift, it downshifts into 3, RPM up to 3k, we would see a direct relationship immediately which I was yesterday. More so than any other test drive. Every time I wanted to speed up or cruise control was downshifting for compensation the temp showed a direct relationship with the torque converter. So 71mph 217 degrees, during and immediately after a shift the temperature temporarily goes up (direct relationship) maybe 5 degrees and then once the truck completes the shift back into OD, shortly thereafter, temperature goes back down to 217, 219. That's more of the direct relationship that I was referring to.

    Now here's the funny part. I've been driving the truck without the IAC plugged in to see if there was a direct correlation with IAC and transmission TEMP. It makes sense that the converter is getting hotter because it's having to stall (lockup) with the crank spinning 700rpm faster than it should be spinning. So I feel yesterday's test drive of over 40 miles mostly freeway showed the temperature stayed a little lower. Problem is that I need to fix the IAC circuit because it's part of the FUEL INJECTION circuit and my performance and gas mileage is suffering by not having it plugged in.

    So basically I 100% agree with @gearcruncher that there is something going on with IAC and torque converter heating up more than it ever has. Pretty coincidental that they're both happening at the same time.

    Million dollar question, why am I not getting voltage on the two outside pins of the IAC connector, RSO RSC????????????????!!!!!!!!!!!!!!! It can't be my ECU!!!! I looked at the wiring diagram again, the inputs the IAC uses are coolant temp, MAF, TPS and maybe CAM and CRANK sensors??? Somehow the VAPOR pressure is apart of that system also and it's the only thing that will not CHECK OUT on my Torque Pro. I cut into the vent line of the tank doing the rear long travel and haven't fixed it. Pretty sure that's why the system won't check. No CEL for it though so never got around to it. Have the fuel hose to do it. Doubt that is the problem.
     

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