Idle staying at 2,000 RPM

Discussion in 'Fox 5.0 Mustang Tech' started by savegoodautonfg, Apr 18, 2007.


  1. savegoodautonfg

    savegoodautonfg New Member

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    1. My idle is set to about 850-900 rpms, and when im driving only sometimes for some reason after about 5 minutes or so, i'll stop and let my foot off the clutch and the rpm will stay at 2,000 rpm and not go down unless i turn the car off and then on again. This is happening too much lately. Any ideas?

    2. This is a different problem but, also, for as long as i can remember when im driving and i let off the gas and take my foot off the clutch and drop it in nuetral or whatever the car's rpm stays up higher then idle then when i come to a complete stop, after a second then it will drop to regular idle.


    any ideas?

    thanks in advance
    #1
  2. savegoodautonfg

    savegoodautonfg New Member

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    To add, i just went outside and checked a few things, when i disconnect the IAC connector absoultely nothing happens the idle speed doesnt change at all.

    is it suppose to right?
    #2
  3. jrichker

    jrichker StangNet's favorite TOOL SN Certified Technician Founding Member

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    You guys with idle problems could same a lot of time chasing your tails if you would go through the Surging Idle Checklist. Over 50 different people contributed information to it. The first post has all the fixes, and steps through the how to find and fix you idle problems without spending a lot of time and money. I continue to update it as more people post fixes or ask questions. You can post questions to that sticky and have your name and idle problem recognized. The guys with original problems and fixes get their posts added to the main fix. :D:
    #3
  4. savegoodautonfg

    savegoodautonfg New Member

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    I looked over it but i was wondering i couldnt find the fix on the 2nd item i mentioned?
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  5. jrichker

    jrichker StangNet's favorite TOOL SN Certified Technician Founding Member

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    Increased idle speed while the car is rolling is a function of the VSS sensor. The idea is to add a little more idle speed as the car slows down to keep the engine from stalling.
    #5
  6. savegoodautonfg

    savegoodautonfg New Member

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    That is normal, and it suppose to do that? IT doesnt actually ever go back to complete regular idle until i am stopped.
    #6
  7. 95_5.0_stang

    95_5.0_stang New Member

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    Sounds to me like ya have a vacuum leak. I had the same problems you do. It was a leak from the upper intake.
    #7
  8. savegoodautonfg

    savegoodautonfg New Member

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    all my vacuum lines are fine, and for the past few months theres a vacuum type noise coming from there, but idle otherwise is fine when sitting still.

    could never find that vacuum leak even if their was one.
    #8
  9. savegoodautonfg

    savegoodautonfg New Member

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  10. 4G-KDMP

    4G-KDMP Member

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    have you checked to see if your throttle cable isn't kinked or cracked anywhere?
    #10
  11. savegoodautonfg

    savegoodautonfg New Member

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    yes its not

    any other ideas guys?

    also:

    To add, i just went outside and checked a few things, when i disconnect the IAC connector absoultely nothing happens the idle speed doesnt change at all.

    is it suppose to?
    #11
  12. AnthonyR23

    AnthonyR23 Member

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    sounds like your iac motor is bad... take it off and give it a good cleaning.. if that doesn't work... then it likely needs to be replaced..
    #12
  13. jrichker

    jrichker StangNet's favorite TOOL SN Certified Technician Founding Member

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    It is supposed to change. Re-read the first post on the Surging Idle Checklist. Then print it off and highlight the sections that are similar to your problems. The checklist contains a section on setting the mechanical base idle. I suggest that you read it and follow the instructions.
    #13
  14. savegoodautonfg

    savegoodautonfg New Member

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    I will do that, but also how is setting the idle gonna make my IAC motor affect the idle. cause now when i disconnect IAC the idle speed does'nt change?
    #14
  15. savegoodautonfg

    savegoodautonfg New Member

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    I will do that, but also how is setting the idle gonna make my IAC motor affect the idle. cause now when i disconnect IAC the idle speed does'nt change?

    UPDATE 5/10/07

    Now it starts to stay at 1,300 rpms until i turn the car off, doesnt do it all the time though.

    i've cleaned IAC, EGR and check TPS Voltage (it's at 1.02)

    anything else?
    #15
  16. jrichker

    jrichker StangNet's favorite TOOL SN Certified Technician Founding Member

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    If the idle speed does not change when you disconnect the IAC, then either you have a vacuum leak or the IAC is defective. Cleaing the IAC does not always work.
    #16
  17. savegoodautonfg

    savegoodautonfg New Member

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    i've had a vacuum leak type sound for a while... if you see one of my thread about intake whistling noise you'll know what im talking about.

    about 5 different mechanics have looked at it. can't figure it out. i even brought it to ford.

    i also checked IAC voltage and it is at what it suppose to be at.

    jritcher, also do you think the IAC maybe being bad could be causing my problem with the RPM's?
    #17
  18. jrichker

    jrichker StangNet's favorite TOOL SN Certified Technician Founding Member

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    The IAB and IAC are the same thing on a 5.0 Mustang. Different years use a different name for the same part.

    IAB/IAC theory of operation:

    The 12 volts is not nearly as important as the ground provided by the computer
    Remember that the computer does not supply power for any actuator or relay. It provides the ground necessary to complete the circuit. That means one side of the circuit will always be hot, and the other side will go to ground or below 1 volt as the computer switches on that circuit.

    [​IMG]

    If the IAB does not seat properly (bent rod inside, bent or worn vavle assembly), it will cause the RPM's to stay high when the electrical signal is disconnected.
    #18
  19. 302RollinHard

    302RollinHard New Member

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    Check and clean your 10 pin connectors. That can make your car idle funky as well.
    #19
  20. savegoodautonfg

    savegoodautonfg New Member

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    So are you possibly telling me that it is possible that my IAC/IAB is fine but that my ground is'nt good?
    #20

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