Pesky High Idle problem preventing 300,000 mile mark

Discussion in 'Chrysler 300' started by jdybber, Nov 30, 2005.

  1. jdybber

    jdybber Guest

    Hello all,
    On my 92 Grand Caravan 3.3 I have a high idle problem that
    consistently trips the Code 25 (IAC circuitry). Idle at startup is
    around 1500 RPM's and moves steadily higher(1850+) as engine warms.
    Here is what I have checked and replaced.
    Idle Air Conntrol Motor
    Cleaned throttle body and plate and replaced gasket.
    Swapped out Engine Control Module(ECM) from another Caravan(exact
    No known vacuum leaks or other gasket leaks
    No other codes found
    The code 25 immediately sets itself even after I disconnect the battery
    for an extended period. I even disconnected the ECM and reconnected.
    It will show the code before I ever start the vehicle again. It sets
    itself when key is in on position and checks signal voltage. I am
    suspecting wiring. Resistance tests appear normal. I would like to get
    this car past 300,000 (only 57 miles to go).
    It starts great and ran very well before this high idle issue. For
    those who know a ton more than me: What would be your next steps if you
    were in my shoes? Thanks
    jdybber, Nov 30, 2005
  2. jdybber

    Raja Guest

    just try one more test, connect an voltmeter across the IACV, measure the
    voltage before ignition on, after ignition on, start and idle (1500) and
    monitor the voltage till 1800 RPM, if the voltage is going higher means
    that IACV is the cause of this problem, and check the wiring harness for
    any shorts, cos you have already replaced the ECU and found the same
    also check if there are any gear/ cluth engage switch/sensor, try
    disconnecting it when the RPM is higher, if the wiring harness is short
    from this sensor, this problem could happen.

    just in case, if you have the diagnostic tool with you, check the value of
    Idle CO adjust multiplier if it has that option.
    Raja, Nov 30, 2005
  3. Test the TPS, which sends the signal that controls the IAC.
    Sharon K.Cooke, Nov 30, 2005
  4. jdybber

    aarcuda69062 Guest

    If the code 25 is resetting after you clear the code and turn the
    key on but before you start the engine, then there has to be an
    open or short circuit somewhere in the IAC circuitry.
    Start at the SBEC and ohm out the wires with the IAC plugged in.
    aarcuda69062, Nov 30, 2005
  5. jdybber

    Steve Guest

    You say no "known" vacuum leaks or other gasket leaks... I suspect
    there's an "unknown" one somewhere :) The code is being set because the
    IAC is losing control of the idle speed for some reason, and apart from
    the IAC itself (motor) a vacuum leak is a high probability.

    Try disconnecting and plugging all the vacuum accessory lines as a test.
    A leaking power brake booster (diaphragm or valving) can cause a huge
    vacuum leak but the booster may still work if the engine can "keep up"
    with the leak. Its harder for the A/C blend doors and other small
    vacuum-operated devices to do this kind of thing because of the small
    hoses involved, but check/plug them for this test anyway. What about the
    PCV valve? If this model has a remote mounted MAP sensor, check its line
    (I imagine it doesn't, but not being intimately familiar with the 3.3 in
    a minivan I thought I'd cover all bases.

    Some engines can develop a vacuum leak into the crankcase- again I'm not
    intimate with the 3.3, but if you can disconnect the PCV valve from the
    crankcase, do so and see if you get a light blow-by out of the
    crankcase. If not, it might be that an internal vacuum leak is
    scavenging the crankcase in addition ot the PCV valve. That *usually*
    increases oil consumption, though, so I consider it unlikely.

    You say you replaced the IAC motor- how is the wiring between the motor
    and the PCM?
    Steve, Nov 30, 2005
  6. jdybber

    jdybber Guest

    Thanks. I started doing some resistance tests last night and found
    that the connector where the IAC motor plugs in is a problem. I should
    get around 52 ohms across windings
    of the motor and I do when the motor is out. I plugged it in and
    started checking downstream at the connector(behind battery) at the
    other end of the wiring harness. When I tested across terminals there
    I received an open until I wiggled the IAC connector wires at the
    motor connector and 'voila' I get the 52 ohms. There is something loose
    in that connector plug and I may just replace the whole harness and
    see if I still get the Code 25 tripped. My guess is I won't. This wil
    bring me back to a baseline to figure what else I need to do as I give
    the IAC motor a chance to set idle correctly. Thanks for your help. I
    will keep in touch on outcome.
    jdybber, Nov 30, 2005
  7. jdybber

    Mike Romain Guest

    It is easy enough to just solder in a replacement plug or just the one
    wire. You don't have to stay OEM, it just needs to make a connection.

    I just had to bypass one wire of the heater blower plug in my Cherokee
    and a really common replacement is the CPS plug.

    That trouble is all too common up here in our rust belt, I use spray
    contact cleaner, then dielectric grease on the plug seals on my TPS,
    CPS, IAC and distributor pick up connections.

    Sometimes all they need is a good clean with a spray contact cleaner.
    They only pass computer signal current (low) so the slightest hint of
    corrosion craps them out.

    The Cherokee's idle jumps to 2500 every couple years and a spray clean
    of the TPS plug fixes it. It only has 310,000 km on it.

    86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
    88 Cherokee 235 BFG AT's
    Canadian Off Road Trips Photos: Non members can still view!
    (More Off Road album links at bottom of the view page)
    Mike Romain, Nov 30, 2005
  8. jdybber

    philthy Guest

    also chech the throttle shaft to see if it's worn out causing a vac leak
    philthy, Dec 3, 2005
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