High idle and revs not coming down | Ford Escort Owners Association (FEOA)
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High idle and revs not coming down

Discussion in '3rd Gen 1997-2002 2.0L SOHC' started by john73, Sep 3, 2019.

  1. john73

    john73 FEOA Member

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    I've read a lot of posts about high rpms and idles but none that are quite like mine.
    I have a 97 2.0 manual transmission. When the IAC is plugged in the RPMs are way up when in neutral coast or at idle but when I unplug the IAC the RPMs are fine and the idle is fine. I have replaced vacuum lines, cleaned both the TB and the MAF , bench tested the IAC with 12 VDC source (works fine) and used starting fluid to find any vacuum leak. No luck. I'm pretty sure I have a vacuum leak. I'll grab a mity Vac and doing some more investigating. Any other ideas or thoughts are much appreciated in advance.
  2. Swift

    Swift FEOA Donator

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    If you look at the iacv from the bottom when unbolted is the plunger thing seated against the metal seat when it is unplugged?
  3. zzyzzx

    zzyzzx FEOA Member

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    Exactly how did you test the IAC?
  4. john73

    john73 FEOA Member

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    OK The IAC is closed completely.

    IAC is receiving 12 V all the time.

    What sensors/signals influence the IAC the most?

    Bad ECU?
  5. rbailin

    rbailin FEOA Member

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    In this thread: https://www.feoa.net/threads/rpm-hang-up-and-increase-when-shifting.97113/#post-907641

    I explained the purpose of the clutch pedal position sensor and the PNP (park neutral position) sensor on the transmission. Basically, when the clutch is engaged *and* the transmission is in gear, the ECU increases the idle speed to prevent stalling.

    If the CPP and PNP are both always open (bad switch or unplugged connector), the ECU would assume that the clutch is always engaged and the transmission is always in gear, so the idle would always be increased.

    You can easily force the ECU to think that the CPP is closed (clutch depressed) by unplugging its connector and shorting the two wire terminals (brown/yellow stripe and green/black stripe) with a small paper clip. The idle should drop to normal.
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  6. denisond3

    denisond3 Moderator Staff Member

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    I once connected a VOM to the IACV in my 92LX 2nd gen Escort. The VOM just showed a flurry of scattered readings. But VOMs work by sampling, and go nuts when seeing a quickly varying signal,, at least the cheap ones like mine do.
    So I connected an oscilloscope to the wires connected to the IACV. The scope showed a more or less square wave of about 2 kilo-cycles per second, and something like 5 volts peak to peak. This was with the engine idling. When the idle speed would wander up or down, the displayed signal would slightly change its 'duty cycle'. I dont know how the 3rd gen Escorts operate their IACV's.

    Somebody with a 3rd gen and a scope should check it out.
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  7. zzyzzx

    zzyzzx FEOA Member

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    This is how I would expect an IAC to work.
  8. john73

    john73 FEOA Member

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    With a Fluke DVM my voltage reads consistently 12 - 14.4 VDC, even when revving the engine and holding the rev for 10 - 15 seconds. I would assume that the voltage should at least fall well below 12 V when revving. I'll hopefully put a scope on it tomorrow.
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  9. john73

    john73 FEOA Member

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    I have a vacuum leak after the throttle body (head side) that I can not locate. I have blocked all the vacuum lines and the car still idles fine. Are there any common areas in the intake, TB, butterfly valve and fuel injector intermediate manifold that are common areas to leak? I tried the soapy water with no luck and now I'll bring out the propane torch. This problem seems to get more and more in depth. Once I find the vacuum leak(s) I'll tackle the problems upstream if they still exist.
  10. rbailin

    rbailin FEOA Member

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    The only places on the intake manifold to block vacuum are:
    1. The port below the TB that goes to the EVAP system.
    2. The PCV port in the back center of the manifold.
    3. The common large vacuum port on the passenger side of the manifold.
    Leaks are common at cylinder #2 of the intake manifold gasket between the IIRC and the cylinder head, but I can't imagine them being large enough to affect the idle speed.

    If, as you said above, the IAC is closed completely, then the engine shouldn't idle at all. If you remove the IAC from the TB and plug the 2 open holes, the engine shouldn't idle at all unless you manually open the TB butterfly or one of the 3 ports mentioned above are open. There just aren't any other significant sources of air to the engine.

    I think that when the IAC is attached and you unplug its connector, it's left in a failsafe mode that allows the engine to idle normally when warmed up.

    Have you tried unplugging the CPP connector on the clutch pedal yet? (If you unplug the other one by mistake, you won't be able to start the car.)
  11. john73

    john73 FEOA Member

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    Thanks for all the help. I've been chasing my tail. Swift was right in the beginning, IAC. It looks like it is closed but that is the problem, Thanks for all the help!
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  12. Swift

    Swift FEOA Donator

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    Just a lucky guess, but some of the symptoms sounded similar to ones I had.
    I have a 2nd gen and I bought a "new" IACV from Advanced, well car kept revving high. I looked in with a flashlight and could see the plunger would not fully seat.
    In the end it took alot of emails and pictures with Wells electronics for them to admit that it was a manufacturing error. They were going to trade out another new one with the one I bought, but they came back and said it was discontinued and they couldn't even get a different manufactures as they were discontinued as well.
    Long story short, I put on a good used 3rd gen IACV with the intake tube from the 3rd gen. Luckily the 2nd gen ecu ran fine with it.
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