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IAC/TPS advice (96 2.7L 4WD MT 143Kmiles

Discussion in '1st Gen. Tacomas (1995-2004)' started by THatt, Oct 5, 2022.

  1. Oct 5, 2022 at 6:05 PM
    #1
    THatt

    THatt [OP] Well-Known Member

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    Have searched and read a ton on this but am asking for advice since I'm still a little lost. Any help appreciated.

    '96 2.7L MT 143K miles
    -Installed scan gauge. Idle at normal op temp was 1200 or so. Truck ran well. Operating temp seems to be 184F per scan gauge.
    -Checked ohms on TPS and got no reading at low feeler gauge checks.
    -Disconnected battery
    -Removed and cleaned throttle body and behind butterfly was coal black, assume habitual gas topping off or just had never been cleaned. Cleaned all the way into plenum.
    -Removed IAC and found it gunked and locked open. Cleaned it thoroughly but did not fully disassemble. Applied 12v dc and it would actuate, seemed no binding. Closed cycle it stops with about 1/16" gap, not sure if that is normal.
    -Did not remove TPS
    -Have replaced hoses, no vacuum leaks or symptoms of such that I can find.
    -Dash pot retracts with vacuum
    -Reassembled everything. Truck is now very responsive and runs great but idle is varible. Cold start I have to pat gas peddle a few times to get it idling since it immediately dies if I don't. Idle after it warms up a little is sometimes 500-600, then 700-800 and once in a while 1000-1100. Overall the idle is too low.

    So my questions are:

    In cleaning the throttle body could I have contaminated or damaged the TPS?
    Could the IAC be locked closed and causing this?
    Any of the symptoms above point to a culprit not already mentioned?

    I am planning on just replacing both the TPS and IAC. Wondering what else could cause this that would have been masked by the previous high idle condition, or is that even possible.
    Thanks for any help.
     
  2. Oct 5, 2022 at 11:01 PM
    #2
    Digiratus

    Digiratus Adventurer

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  3. Oct 5, 2022 at 11:24 PM
    #3
    YotaGangYotaGang

    YotaGangYotaGang PreRunners are wannabe 4x4’s

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    checkout the plunger if it retracts at the bottom of the iacv
     
  4. Oct 6, 2022 at 8:25 AM
    #4
    Andy01DblCabTacoma

    Andy01DblCabTacoma Well-Known Member

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    Check the throttle cable tension. It's possible for it to be too loose or too tight. Too tight will cause a high idle, too loose shouldn't drop the idle, but might contribute to having to push the pedal to keep it alive on a cold start.

    It's been my experience, that cleaning the IAC isn't a magic fix, and most people end up replacing it to rule it out as an issue even after testing them.
     
  5. Oct 6, 2022 at 4:13 PM
    #5
    nagorb

    nagorb Should be a dang perma mod

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    If you removed the iac and cleaned and only cleaned the ports, it may not be fully clean. I'd suggest removing the solenoid, two screws covered in fipg, and cleaning.
     
  6. Oct 7, 2022 at 6:00 PM
    #6
    Potomus Pete

    Potomus Pete Love my little truck

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    All kinds 3 inch body lift/2 1/2 suspension lift. 31/11 1/2/15 tires All work done by myself for years. The only work performed by mechanic was fuel pumps. I also have a 90 Mustang 350 hp and I can never understand how come my Tacoma gets more respect Just got a 99 Jeep TJ that I rebuilt, and painted in the garage
    Carb cleaner can kill a TPS. I have done two of them, but not on a Tacoma
     
  7. Oct 7, 2022 at 8:56 PM
    #7
    O'Silver_Taco

    O'Silver_Taco Well-Known Member

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    If you're gonna replace iac....while in same area you might pull the egr valve off.....shoot with carb cleaner and check for actuation....
    Make sure that port isn't carbon clogged or that temp sensor hole on intake plenum....

    Dirty, sticky egr with cause weird idle probs.....and if never cleaned....pretty dirty at 150K.....



    Before you do that, score a pair of oem egr gaskets......old ones are gonna be cooked....and the ones from the auto stores dont fit right.....those need to be oem from a dealer.....

    U have to score the gasket for the iac anyways....

    And for a good measure....a new pcv valve and grommet....
     
    Last edited: Oct 7, 2022
  8. Oct 9, 2022 at 3:21 PM
    #8
    THatt

    THatt [OP] Well-Known Member

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    Thanks for the suggestions.

    Have ordered new TPS, TB gasket, IAC, IAC gasket, EGR gasket, intake manifold gasket set and PCV grommet.

    Planning to pull the lot, clean and reinstall. Have completely replaced vacuum lines. Truck is running great but just some idle issues. The IAC was gunked and stuck open, probably accounts for the previous constant high idle (1100-1200). I'm guessing the half "cleaned" IAC is now inconsistent, may be sticking every now and then. Or I may have gotten some throttle body cleaner in the TPS. TPS ohms out properly via Haynes manual feeler gauge test. I misspoke on that in first post but am replacing it anyway. Went back and verified. I also verified I am getting vacuum everywhere I should and at rpms, also per Haynes manual.

    Pondering putting in a catch can. Any advice to give on that? Hate to clean all that plenum up and just gunk it again.

    Will update when I get parts in and installed. Thanks again.
     
    Potomus Pete likes this.
  9. Oct 9, 2022 at 9:27 PM
    #9
    O'Silver_Taco

    O'Silver_Taco Well-Known Member

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    Some use junk parts.....quick fix or whatever...
    going thru swapping back over to oem can be like a game....
    and u end up with an extra emergency part to boot.....

    If you are running anything but a toyota oem MAF, thats not advisable...
    because of its direct ecm connection....junk one could fry ecm.....
    it provides ground for ignition circuit in start sequence.....

    Yotas run really well using their own sensors.....
    all the rest of the vehicle sometimes ....Oem,... sometimes not....
     
    Last edited: Oct 9, 2022
  10. Oct 17, 2022 at 4:26 PM
    #10
    THatt

    THatt [OP] Well-Known Member

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    Appreciate the help. Got all my parts in to replace TPS, IAC, EGR gaskets, Intake manifold & plenum gaskets. Have throttle body off and plenum. Found intake manifold requires removing banjo fittings from fuel pump to fuel rail. (pictured below). Any advice on how to remove these? Do I need more parts? Have Haynes manual and fixing to read up on it as much as I can but sure would like to hear some thoughts from anyone who has done this portion.
    [​IMG]


    Also, should I remove this sensor on the plenum prior to cleaning it?
    [​IMG]

    Lastly, should I just stop where I am at, clean the plenum and back out leaving the intake alone?

    Thanks for any advice.
     
  11. Oct 17, 2022 at 6:20 PM
    #11
    THatt

    THatt [OP] Well-Known Member

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    Ok fellas. I'm down to this. I did not follow the procedure to remove the fuel pressure prior to beginning disassembly. Haynes manual says to disconnect battery (done), removed EFI in fuse box (done) but did not/cannot now crank engine to let it stall. I've gotten everything taken off except the intake manifold and the fuel line from the filter to fuel rail. My main questions are:

    How can I relieve fuel pressure prior to disconnecting banjo fitting from fuel rail?
    Can I just ease that banjo fitting loose and let it drip?

    I believe I can remove the intake if I can disconnect the banjo fitting on the fuel rail. Top circled fitting in first picture above.

    Thanks for any help.
     
  12. Oct 19, 2022 at 5:27 PM
    #12
    THatt

    THatt [OP] Well-Known Member

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    Well maybe some don't know it so here goes:

    Truck sat uncranked from Sunday eve till yesterday eve. Opened gas cap for a bit. Got banjo fitting to break loose on fuel rail, maybe two drops of gas came out so that was needless worry. Also disconnected hose to fuel regulator valve.

    Sensor in plenom is EGR temp.

    Cleaned ports, plenum and intake. Used diesel, xylene and throttle body cleaner, pretty much in that order. Was fairly caked throughout with carbon/oil but this is mostly a short trip truck all these years. Had seen a post here from a few years ago about this cleaning but it omitted the fuel line running through the intake between pipes and how to address it.

    Ordered and today received a catch can so that's going on too.

    Planning to replace TPS, IAC tomorrow and put all this stuff together.

    Have taken pictures of entire process, mostly to help back out on assembly. Glad to post if it helps anyone.
     
  13. Oct 23, 2022 at 3:58 PM
    #13
    THatt

    THatt [OP] Well-Known Member

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    So here is where I am at.
    Idle at normal op temp is 950-1000 after all the work and adjusting.
    Throttle body has zero play in it, butterfly valve closes well but I can see a tiny sliver of light through it. Have adjusted set screw in so that butterfly closes completely as far as it will go then turned set screw back 1/4 turn to keep butterfly from sticking. TPS is adjusted to 10 at closed throttle per scangauge. IAC is working properly. Have replaced all vacuum hoses. Checked everything I can think of. Power steering fluid is up to full, brake booster line is good as well as brakes so neither of those is an issue. Engine temp sensor is good on scangauge so that can't be it. Used an unlit propane torch as well as throttle body cleaner to check for any intake or hose leaks and have found none. Cleaned MAF. EGR is good, PCV valve is good and new grommet, dash pot is good. Truck runs like a scalded monkey now, very responsive.

    Previous history with high idle (1100-1200) found original IAC locked open when I cleaned throttle body. Got it working again but within a few days truck had intermittent idle, down to 500 and would stall at cold start without a little peddle. This time when I cleaned entire intake I found the original IAC stuck closed, so all that low idle makes sense.

    Can anyone suggest what I may be overlooking? Sure would like to get this thing idling down to 800 rpm or so.

    Cleaning ports, two on right yet to go.
    [​IMG]
    Plenum before cleaning
    [​IMG]
    Cleaning intake mainfold
    [​IMG]
    After cleaning
    [​IMG]
    Piddled on it from Monday till Thursday as I had time
    [​IMG]
    Installed a new IAC and TPS
    [​IMG]
    Installed a catch can to try to keep it all clean going forward
    [​IMG]
     
    Last edited: Oct 23, 2022
  14. Oct 23, 2022 at 4:27 PM
    #14
    THatt

    THatt [OP] Well-Known Member

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  15. Oct 23, 2022 at 9:44 PM
    #15
    O'Silver_Taco

    O'Silver_Taco Well-Known Member

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    What about the egr valve.....if intake is carboned up....so will the egr valve....
     
  16. Oct 24, 2022 at 1:36 AM
    #16
    THatt

    THatt [OP] Well-Known Member

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    Cleaned EGR too while I was in there. Would blockage there cause higher idle? Pipe from exhaust manifold to EGR had some carbon in it but didn't look clogged. That pipe is about the only thing upstream of the block on the intake side that I didn't clean. Also verified vacuum at each throttle port per Haynes manual per RPM. Thank you for the suggestions.
     
  17. Oct 24, 2022 at 5:11 AM
    #17
    O'Silver_Taco

    O'Silver_Taco Well-Known Member

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    That tube doesnt seem to clog to any detriment....at least mine was fine at the 170K mark....
    the valve was pretty crusty tho......
     
  18. Dec 1, 2022 at 2:56 PM
    #18
    Rastopher

    Rastopher Well-Known Member

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    I ordered a new throttle body assembly for my 2002 2.7 3rz-fe last year and haven’t got to put it in yet. I find it really interesting that all these people recommend a throttle body re-bore if you can see light through the throttle when it’s closed.
    Here’s my brand new, untouched one for your comparison. Not really trying to make a huge statement here but something doesn’t line up.

    15FDAFCB-4243-4FA2-80A8-679EB3FF580F.jpg
    FDDA7D29-C7C8-492E-8045-D2B9E8686A1E.jpg
    D3267B9E-FE7B-4C04-BA54-D8FDAEF35DBC.jpg
    D18B0229-3CA1-4CFF-977C-6E7DC9F5A64C.jpg
    9BBC401F-4293-4BFE-BCA2-9A9E160C9D04.jpg
    238B1D95-F4F0-4EC7-9031-E680AD4CC15F.jpg
    5DDADEE8-F19B-4A1F-9941-3564DBCB7CF9.jpg
     
    THatt[OP] likes this.
  19. Dec 1, 2022 at 3:48 PM
    #19
    THatt

    THatt [OP] Well-Known Member

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    I get it. Pretty much what I am seeing on my truck. I'm still idling at 950-1000 rpm. Better response, cranks perfectly hot or cold and MPG seems good, 19-21.5. I put an aftermarket IAC in, not cheapest but still aftermarket. I figured out how to get the original OEM cleaned up after I got everything back together. I may put it back on just to see if the idle changes. Either way, it's better than it was before and I can live with it. Thanks for the pictures and good luck with your truck.
     
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  20. Oct 26, 2024 at 4:44 AM
    #20
    THatt

    THatt [OP] Well-Known Member

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    Updating and closing out this thread since I just referenced it. Replaced IAC with OEM and truck runs perfectly for about two years now. Aftermarket had larger air port so rpm’s were higher with it in any position. Aftermarket also lacked thermal spring which I believe allows gradual throttle reduction as warming occurs with OEM. I tried putting old OEM unit back in truck for a while and it worked intermittently. Either valve was still sticking despite thorough cleaning or the coil on the silenoid was weakened. When I tried bench testing the old versus new OEM using 12v to accurate them the new OEM unit would close with a forceful click while the old unit was slower and quieter as if dragging. My thoughts are they just wear out of the cleaner degraded the coil in some manner. Lots of folks suspect throttle body bore, flapper wear. Was not the issue with mine and you can see slight daylight through it when it’s fully closed with dash pot plunger retracted. Still 700rmp per spec.
     

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