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P0172 Solved

Discussion in 'Minivans · Pacifica' started by CudaPete, Dec 14, 2017.

  1. CudaPete

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    Here is how I fixed a rough idle condition and code p0172 on my 02 Grand Caravan;
    • Remove and clean throttle body including IAC valve.
    • Replace upstream O2 sensor
    • Adjust throttle stop to increase idle, This compensates for mechanical wear on screw tip over the years
    • Add fuel injector cleaner to tank to clean any carbon that may have built up while runniing rough
    It is a multi-step solution for the repair and you need to do all of these steps.
     
  2. ImperialCrown

    Level III Supporter

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    I might agree with all, but would not tamper with the minimum air adjustment screw unless one has the special tool (orifice) and a way of fully seating the IAC as in the service manual procedure before adjusting. It is NOT meant as an idle adjustment screw.
    The PCM sets idle speed according to conditions. If it requires more air at closed throttle, it simply opens the IAC. If it requires less, it closes the IAC. The PCM constantly regulates idle speed and will compensate for load changes like: A/C compressor engagement, P/S pump loads, shifting in or out of gear, etc. by opening or closing the IAC. If there are idle speed issues, simply turning the screw may be masking another problem. A 'rough' idle (misfire) can sometimes feel like a 'slow' idle.
    I have not noticed the mechanical flattening or wear of the air screw tip that you mention. I suppose that a very high-mileage vehicle might exhibit minor wear on the hardened screw tip?
    If you replace an O2 sensor, use an OEM part.
    The only 'safe to use' fuel system cleaner ever mentioned in a Chrysler service bulletin is Techron. Although fuel quality may vary by location and supplier, I might use a bottle a year for maintenance purposes.
     
    Dave Z likes this.
  3. CudaPete

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    See, that's the thing. That hardened scew hits that non-hardened stop and that's what wears. You have to look very closey. Remember this slams closed every time you take your foot completely off the gas. The adjustment of the screw is so fine but makes a big difference. We adjusted it with engine off so the IAC should be fully closed. There needs to be a certain amount of leakage around the throttle body disc to work properly in conjunction with the IAC. The IAC alone cannot flow enough air by itself even fully open. I've read other posts where just replacing the O2 sensor did not solve the problem that's why I believe it is a multi-step solution. .
     
    Dave Z likes this.

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