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Stumbling under idle/low rev. 97 XJ 4.0

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  • Stumbling under idle/low rev. 97 XJ 4.0

    Been putting this off for awhile, its time I fixed it.

    Its in my 97 XJ.

    I turn the Jeep on, let it run briefly, if I let it sit at idle for a minute, itll start to stumble, drop idle RPM, at some points almost completely stall out, but never quite that far. It will stumble until I give it a healthy amount of throttle, where it seems to clear out, almost a backfire-ish sound coming from the engine bay as it clears and struggles to rev up, but not nearly as loud. At times it will continue to stumble under power if its light power...if I really lay into it I can get it to clear and regain normal idle RPM.

    The jeep runs fine on the highway/driving normally on the road, its only when I let it drop down to idle-ish RPMs, say sitting at a stop light or in my driveway, that it will start to act up like this. On the trail in 4low if im trail riding really slow this also comes up, which is super annoying.

    Before I just start throwing random money at it with a typical tune up and whatever else, what could I be looking at?

    Been a long time since I did any diagnosis like this so I am a bit rusty on my sensors. Thanks guys
    - Will


    Originally posted by fizzy
    or am asians pants not a read end lol.
    Originally posted by DizzDizz
    aliens probed my husband

  • #2
    Idle air control sensor. Right on the throttle body, the sensor controls air flow through throttle body and makes minor adjustments to keep the vehicle running during low RPMs, when the IAC goes bad, the vehicle will stall out or run poorly at low RPMs.
    Last edited by Buffalo Phil; 05-16-2013, 08:22 AM.
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    Official Space Shuttle Door Gunner of the Chechnyan Space Program

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    • #3
      The IAC has been changed in the last couple years. I suppose I can try cleaning it
      - Will


      Originally posted by fizzy
      or am asians pants not a read end lol.
      Originally posted by DizzDizz
      aliens probed my husband

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      • #4
        Mine went bad in a year and a half. See what cleaning it does.

        Wouldn't hurt to clean out the throttle body as well.
        Last edited by Buffalo Phil; 05-16-2013, 01:22 PM.
        sigpic
        Official Space Shuttle Door Gunner of the Chechnyan Space Program

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        • #5
          Map sensor?
          2000 xj 4.5 clayton longarms with wontons with a touch of
          97' zj
          2012 surbra imperza DD
          im a motivation machine like the hammer and sickle in communism

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          • #6
            Tpm sensor
            Don't Panic

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            • #7
              I had that issue with my buddys truck.it was the cps.I put one it for him it lasted a week then went bad again.changed out with a dealer cps.been fine since.

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              • #8
                so change all my sensors. got it. hahah
                - Will


                Originally posted by fizzy
                or am asians pants not a read end lol.
                Originally posted by DizzDizz
                aliens probed my husband

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                • #9
                  stop by I can put the scope on it and read the sensor outputs not hard just probe the wires.
                  Doesn't sound like a CPS.
                  Sounds to me an IAC valve.
                  Basically an idle air control valve is a second throttle plate that the computer operates to make it idle. I've had them go bad in under a year.
                  Quick and dirty test.
                  Pull it out put your finger over the hole and start the car and watch it move if it is not moving it is broken.
                  My boss has a tool you can plug in and operate them manually.

                  Another thing make sure the actual throttle plate is clean if there is build up it can cause some of those issues too. Same with vacuum leaks etc.

                  After that it can be a lot of other things.

                  And I have a 97 XJ 4.0 if you want to try swapping parts.

                  I'll be in my garage tonight.
                  RCrocs #123 Brown CJ-5
                  www.offroadcustomcreations.com

                  Sponsors:
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                  • #10
                    Clean the plunger hole out too Will on the IAC and douche the throttle body out while you are at it.

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                    • #11
                      I'm not sure I can come by tonight, I have a lot of work to catch up on before I am busy the weekend and leaving next week mid week for cali (wednesday). I'd love to come by another time though and figure out wtf is wrong with this thing. Thanks Justin.
                      Lemme know when works for you and I will try and work my schedule to it.

                      Originally posted by customcreationsllc View Post
                      stop by I can put the scope on it and read the sensor outputs not hard just probe the wires.
                      Doesn't sound like a CPS.
                      Sounds to me an IAC valve.
                      Basically an idle air control valve is a second throttle plate that the computer operates to make it idle. I've had them go bad in under a year.
                      Quick and dirty test.
                      Pull it out put your finger over the hole and start the car and watch it move if it is not moving it is broken.
                      My boss has a tool you can plug in and operate them manually.

                      Another thing make sure the actual throttle plate is clean if there is build up it can cause some of those issues too. Same with vacuum leaks etc.

                      After that it can be a lot of other things.

                      And I have a 97 XJ 4.0 if you want to try swapping parts.

                      I'll be in my garage tonight.
                      - Will


                      Originally posted by fizzy
                      or am asians pants not a read end lol.
                      Originally posted by DizzDizz
                      aliens probed my husband

                      Comment


                      • #12
                        For what its worth i think its not the iac. Seemed liked a fuel issue when ive witnessed it

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                        • #13
                          Bring it over before wheeling tomorrow
                          I don't always drink orange juice, but when I do, I prefer to chew it. #madpulp

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