Idle staying at 2,000 RPM

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


  1. HISSIN50

    HISSIN50 "How long does it take to get help in here? SN Certified Technician

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    There is still a difference. As you saw, mine will slow down at 1500 RPM for a tick. It's not a situation where it hangs and it's for a fraction of a second. The falling of RPM simply slows down as it approaches 1500 RPM, and then it falls back to idle. This was where I was thinking others could offer advice about how their particular cars act, as not every car will fall to idle as mine does (or yours does).

    The car wanting to stall when cold is still problematic. Perhaps JRcihker has further info or you can revisit his old posts about checking the IAC wiring to ensure it's doing what it should. I'd be going off the cue that the IAC doesnt work when cold. Once that's sorted out, I'd worry about the hang (because fixing the primary issue will likely fix the secondary [hang]).

    Good luck.
     
    #61
  2. savegoodautonfg

    savegoodautonfg New Member

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    ok i know i check the voltage and everything going to the IAC. IAC is clean as hell because its BRAND NEW. I went through all his steps on the checklist and still having the problem.

    JRITCHER please reply if you can to help me figure this out..

    thanks alot buddy.
     
    #62
  3. jrichker

    jrichker StangNet's favorite TOOL SN Certified Technician Founding Member

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    I haven't been following your efforts very closely, so I may have missed something.
    A short recap of what you have tested, adjusted and replaced and the order that you
    did the work would be very helpful. That way I won't advise you to duplicate something
    you have already done.
     
    #63
  4. savegoodautonfg

    savegoodautonfg New Member

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    bASICALLY i've done everything and check everything on your thread about surging idle checklist IN ORDER. i really have.

    Cleaned everything (brand new IAC) , tried new setting the idle thing, EVERYTHING

    I am getting a CEL light for code 11 first, then 91.

    I know its about something about running rich. I dont know how from what I did it could be running rich.

    Thanks,

    -Nick
     
    #64
  5. savegoodautonfg

    savegoodautonfg New Member

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    I'm out of ideas guys.

    List of what i've changed:

    1. IAC (Brand New)
    2. ECT (Brand New)
    3. ACT (Brand New)
    4. TPS (Brand New)

    My car idle has been sticking at 2,000 rpm again after it hasnt done it for weeks after i cleaned everything. it only did it a few times but still does it until i turn car off and on.

    As soon as i turn car back on it's not sticking anymore.

    Also to add:

    It always sticks at 1,500 and then goes back to idle or goes to 1,000rpm and idles there.

    I cleared engine codes 3 or 4 days ago and i pulled them again yesterday and got 11,31,51,54,66,91

    Code 51: ECT and ACT has been replaced.

    Code 66: Tested the MAF Sensor

    Black and Red wire- 11.86 volts

    Pin C and D- .86 volts at idle

    When i disconnect the MAF Sensor doesnt seem to affect the idle like i feel it used to.

    Code 91: Vacuum Hoses have been recently replaced with silicone hoses and o2 sensors are fine and have been checked.
     
    #65
  6. jrichker

    jrichker StangNet's favorite TOOL SN Certified Technician Founding Member

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    That's a TPS kind of problem. I don't know what to tell you but to check the TPS voltages when it is acting up.
    Check the TPS ground carefully.

    Some basic checks you can make to be sure that the sensor is getting power & ground:
    Note that all resistance tests must be done with power off. Measuring resistance with a circuit powered on
    will give false readings and possibly damage the meter.

    Check the resistance between the black/white wire on the MAP/BARO sensor and then the black/white wire on
    the EGR and the same wire on the TPS. It should be less than 1 ohm. Next check the resistance between the
    black/white wire and the negative battery cable. It should be less than 1.5 ohm.
     
    #66
  7. savegoodautonfg

    savegoodautonfg New Member

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    I will do that next time it acts up.

    What about the codes im still getting even though i've replaced the sensors and such?
     
    #67
  8. jammer84_03

    jammer84_03 New Member

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    with the car sticking at 1500 while comming to stop is built into the programming on the computer. it was made to not drop the rpm immediately and cause more strain on the trans and engine. aem actually has this as a programable option where it wont do it after you go below rolling at 25mph. i believe this is based exactly off of original program.
     
    #68
  9. jrichker

    jrichker StangNet's favorite TOOL SN Certified Technician Founding Member

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    Sorry I didn't read your post more carefully. The extra codes are a definite clue to your problem.

    CODE: 31 (KOEO) - EVP circuit below minimum voltage. Vref (5 volt reference voltage supplied
    by the computer) missing or broken wire or bad connection in circuit. Use a DVM to check for
    5 volts on the orange/white wire. If it is missing, look for +5 volts at the orange/white wire
    on the TPS or MAP sensor located on the firewall near the center of the car. Use the black/white
    wire for the ground for the DVM.
    With the sensor removed from the EGR and still connected, press the plunger and watch
    the voltage change on the brown/lt green wire. Pull the passenger side kick panel and
    measure the voltage at the computer. You will need to remove the plastic cover over
    the wires and probe them from the backside. A safety pin may prove very useful for this task.
    Use pin 27, EVR input (brown/lt green wire) and pin 46, signal ground (black/white wire) to
    measure the voltage. The orange/white wire is Vref and should always be 5 volts -/+ .25 volt.
    Be sure to measure Vref at the EGR sensor to rule out any broken wires or bad connections.

    Code 51 Engine Coolant Temperature (ECT) sensor signal is/was too high -
    Possible bad ECT sensor, or wiring. Possible missing signal ground –
    black/wire wire broken or bad connection. With the power off, measure the
    resistance between the black/white wire and battery ground. You should see
    less than 1 ohm. Check the same black /white wire on the TPS and MAP
    sensor. More than 1 ohm there and the wire is probably broken in the harness
    between the engine and the computer. The 10 pin connectors pass the
    black/white wire back to the computer, and can cause problems.

    Pin 7 on the computer - ECT signal in. at 176 degrees F it should be .80 volts

    Voltages may be measured across the ECT by probing the connector from the rear.
    Use care in doing it so that you don't damage the wiring or connector.

    50 degrees F = 3.52 v
    68 degrees F = 3.02 v
    86 degrees F = 2.62 v
    104 degrees F = 2.16 v
    122 degrees F = 1.72 v
    140 degrees F = 1.35 v
    158 degrees F = 1.04 v
    176 degrees F = .80 v
    194 degrees F = .61
    212 degrees F = .47 v
    230 degrees F = .36 v
    248 degrees F = .28 v

    Ohms measures at the computer with the computer disconnected, or at the sensor with the sensor disconnected.

    50 degrees F = 58.75 K ohms
    68 degrees F = 37.30 K ohms
    86 degrees F = 27.27 K ohms
    104 degrees F = 16.15 K ohms
    122 degrees F = 10.97 K ohms
    140 degrees F = 7.60 K ohms
    158 degrees F = 5.37 K ohms
    176 degrees F = 3.84 K ohms
    194 degrees F = 2.80 K ohms
    212 degrees F = 2.07 K ohms
    230 degrees F = 1.55 K ohms
    248 degrees F = 1.18 k ohms

    Diagram courtesy of Tmoss & Stang&2birds

    [​IMG]

    See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host) for help on 88-95 wiring http://www.veryuseful.com/mustang/tech/engine/

    http://www.veryuseful.com/mustang/tech/engine/images/IgnitionSwitchWiring.gif

    http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

    http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif

    Code 54 – ACT sensor out of range. Broken or damaged wiring, bad ACT sensor.
    Note that that if the outside air temp is below 50 degrees F that the test for the ACT can be in error.

    Check the resistance of the black/white wire to battery ground. If it is less than 1.5 ohm,
    it is good. If it is more than 1.5 ohm, the black/white wire has bad connections or a broken wire.
    Always take resistance measurements with the circuit powered off.

    Then check the resistance of the ACT sender located in the #5 intake runner on most 5.0 stangs.

    ACT & ECT test data:

    The ACT & ECT have the same thermistor, so the table values are the same

    Pin 7 on the computer - ECT signal in. at 176 degrees F it should be .80 volts

    Pin 25 on the computer - ACT signal in. at 50 degrees F it should be 3.5 volts. It is a good
    number if the ACT is mounted in the inlet airbox. If it is mounted in the lower intake manifold,
    the voltage readings will be lower because of the heat transfer. Here's the table :

    68 degrees F = 3.02 v
    86 degrees F = 2.62 v
    104 degrees F = 2.16 v
    122 degrees F = 1.72 v
    140 degrees F = 1.35 v
    158 degrees F = 1.04 v
    176 degrees F = .80 v
    194 degrees F = .61

    Ohms measures at the computer with the computer disconnected, or at the sensor with the sensor disconnected.
    50 degrees F = 58.75 K ohms
    68 degrees F = 37.30 K ohms
    86 degrees F = 27.27 K ohms
    104 degrees F = 16.15 K ohms
    122 degrees F = 10.97 K ohms
    140 degrees F = 7.60 K ohms
    158 degrees F = 5.37 K ohms
    176 degrees F = 3.84 K ohms
    194 degrees F = 2.80 K ohms

    Code 66 MAF below minimum test voltage. Insufficient or no voltage from MAF.
    Dirty MAF element, bad MAF, bad MAF wiring, missing power to MAF. Check for missing
    +12 volts on this circuit. Check the two links for a wiring diagram to help you find the red wire for
    computer power relay switched +12 volts. Check for 12 volts between the red and black
    wires on the MAF heater (usually pins A & B). while the connector is plugged into the MAF.
    This may require the use of a couple of safety pins to probe the MAF connector from the back side of it.

    There are three parts in a MAF: the heater, the sensor element and the amplifier. The heater
    heats the MAF sensor element causing the resistance to increase. The amplifier buffers the
    MAF output signal and has a resistor that is laser trimmed to provide an output range
    compatible with the computer's load tables.

    The MAF element is secured by 2 screws & has 1 wiring connector. To clean the element,
    remove it from the MAF housing and spray it down with electronic parts cleaner or non-inflammable
    brake parts cleaner (same stuff in a bigger can and cheaper too).

    The MAF output varies with RPM which causes the airflow to increase or decease. The increase
    of air across the MAF sensor element causes it to cool, allowing more voltage to pass and
    telling the computer to increase the fuel flow. A decrease in airflow causes the MAF sensor
    element to get warmer, decreasing the voltage and reducing the fuel flow. Measure the MAF
    output at pins C & D on the MAF connector (dark blue/orange and tan/light blue) or at pins
    50 & 9 on the computer. Be sure to measure the sensor output by measuring across the
    pins and not between the pins and ground.


    At idle = approximately .6 volt
    20 MPH = approximately 1.10 volt
    40 MPH = approximately 1.70 volt
    60 MPH = approximately 2.10 volt

    Check the resistance of the MAF signal wiring. Pin D on the MAF and pin 50 on the computer
    (dark blue/orange wire) should be less than 2 ohms. Pin C on the MAF and pin 9 on the
    computer (tan/light blue wire) should be less than 2 ohms.

    There should be a minimum of 10K ohms between either pin C or D on the MAF wiring
    connector and ground. Make your measurement with the MAF disconnected from the wiring harness.


    See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host)
    for help on 88-95 wiring http://www.veryuseful.com/mustang/tech/engine/

    Ignition switch wiring
    http://www.veryuseful.com/mustang/tech/engine/images/IgnitionSwitchWiring.gif

    Fuel pump, alternator, ignition & A/C wiring
    http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

    Computer,. actuator & sensor wiring
    http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif

    Fuse panel layout
    http://www.veryuseful.com/mustang/tech/engine/images/MustangFuseBox.gif

    Vacuum routing
    http://www.veryuseful.com/mustang/tech/engine/images/mustangFoxFordVacuumDiagram.jpg

    Code 41 or 91 - O2 indicates system lean. Look for a vacuum leak or failing O2 sensor.

    The computer sees a lean mixture signal coming from the O2 sensors and tries to
    compensate by adding more fuel. Many times the end result is an engine that runs pig
    rich and stinks of unburned fuel.

    The following is a Quote from Charles O. Probst, Ford fuel Injection & Electronic Engine control:
    "When the mixture is lean, the exhaust gas has oxygen, about the same amount as the
    ambient air. So the sensor will generate less than 400 Millivolts. Remember lean = less voltage.

    When the mixture is rich, there's less oxygen in the exhaust than in the ambient air , so voltage
    is generated between the two sides of the tip. The voltage is greater than 600 millivolts.
    Remember rich = more voltage.

    Here's a tip: the newer the sensor, the more the voltage changes, swinging from as low
    as 0.1 volt to as much as 0.9 volt. As an oxygen sensor ages, the voltage changes get
    smaller and slower - the voltage change lags behind the change in exhaust gas oxygen.

    Because the oxygen sensor generates its own voltage, never apply voltage and never
    measure resistance of the sensor circuit. To measure voltage signals, use an analog voltmeter
    with a high input impedance, at least 10 megohms. Remember, a digital voltmeter will
    average a changing voltage." End Quote

    Testing the O2 sensors
    Measuring the O2 sensor voltage at the computer will give you a good idea of how well
    they are working. You'll have to pull the passenger side kick panel off to gain access to the
    computer connector. Remove the plastic wiring cover to get to the back side of the wiring.
    Use a safety pin or paper clip to probe the connections from the rear.
    The computer pins are 29 (LH O2 with a dark green/pink wire) and 43 (RH O2 with a dark
    blue/pink wire). Use the ground next to the computer to ground the voltmeter.

    Note that all resistance tests must be done with power off. Measuring resistance
    with a circuit powered on will give false readings and possibly damage the meter.
    Do not attempt to measure the resistance of the O2 sensors, it may damage them.


    Testing the O2 sensor wiring harness
    Most of the common multimeters have a resistance scale. Be sure the O2 sensors are
    disconnected and measure the resistance from the O2 sensor body harness to the pins on the computer.



    The O2 sensor ground (orange wire with a ring terminal on it) is in the wiring harness for
    the fuel injection wiring. I grounded mine to one of the intake manifold bolts

    Replace the O2 sensors in pairs if replacement is indicated. If one is weak or bad, the other one probably isn't far behind.


    What to look for to fix your problem:
    The 51 & 54 codes both point to a bad computer signal ground. This would allow the
    voltage to be higher that it should be normally.The black/white wire is signal ground for
    the TPS, EGR, ACT, ECT and BARO signals. The BARO sensor hasn't poped up a
    code, so the problem is in the engine wiring harness, most likely in the 10 pin connectors.
    [​IMG]

    Clean the 10 pin connectors with electronic parts cleaner or non-inflammable brake
    parts cleaner (same stuff in a bigger can and cheaper too). The white connector center pin
    marked SIG-RTN in the diagram is the black/white wire signal ground. Use a test light
    with one lead connected to the battery and the other to the black/white wire on
    the TPS or ECT. You will probalbly need to disconnect the sensor to get a good connection.
    Wiggle the wiring and the 10 pin connectors and watch to see if the light flickers. If it still
    flickers after cleaning the 10 pin connectors, you have a broken black/white signal ground wire.

    MAF code 66: Do you have a cold air intake system other than the factory stock system?
    These can cause problems and the fix is often to rotate the MAF housing to smooth
    out the airflow through the MAF.

    If you measured the MAF output voltage across the C & D pins like it is supposed to be
    done and got .86 volts, you may have wiring problems. Never connect the voltmeter
    leads to ground when checking the MAF. Disconnect the MAF connector and then
    access the computer by removing the passenger side kick panel and disconnect the computer connector.
    There is a 10 MM bolt that holds it in place. Measure the resistance between pin 9
    on the compute and pin C on the MAF wiring harness connector. Measure the resistance
    between pin 50 on the compute and pin D on the MAF wiring harness connector. Both should
    read less than 1.5 ohms. More than than that is an indication of wiring problems.


    The following is a view from the computer side of the computer connector.
    [​IMG]

    The code 91 is probably a vacuum leak. However, it may disappear after you fix the MAF problems.
     
    #69
  10. savegoodautonfg

    savegoodautonfg New Member

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    Jritcher, i pmed you.
     
    #70
  11. savegoodautonfg

    savegoodautonfg New Member

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    Jritcher can you please check my P.M.
     
    #71
  12. jrichker

    jrichker StangNet's favorite TOOL SN Certified Technician Founding Member

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    I have basically quit answering requests for help via PM's and emails. I find that the input and insight
    that other people bring to the discussion is very valuable. They will often see or think of things that
    did not occur to me.

    The following description works on the basis of you having an understanding of basic electrical
    circuits. If you don't understand it, then trying to explain what electricity is, what resistance is
    and how electricity flows through a circuit is beyond what can be done in this reply.

    The 51 & 54 codes point to a loss of signal ground. The TPS sensor is a variable resistor with one leg
    tied to VREF and the other leg tied to ground. Its function is to provide a means of supplying a voltage
    that increases as the throttle opens. With a missing or poor quality signal ground, there is no way for the
    voltage to decrease to the level that tells the computer that the throttle is closed and it should act
    accordingly. With a poor ground, instead of seeing .7 volts, it might see 1.5 volts and think you were
    cruising and increase the injector pulse width and airflow through the IAB.

    [​IMG]

    As to where you can find the signal ground wire, the black/white wire is signal ground for the TPS, EGR,
    ACT, ECT and BARO signals. Look closely at the diagram Tmoss provided that shows the whole
    computer system layout. You will see that the black/white signal ground is connected to a number of things.

    In your case, the TPS, ACT & ECT all seem to have a loss of signal ground. That means the problem is
    limited to the engine fuel injector harness. The 10 pin connector on the engine side of the fuel injector
    harness is a good place to start a careful inspection for corrosion, broken wiring, and bad connections.
    The wiggle test using a test lamp would be very useful in locating the problem.
     
    #72
  13. savegoodautonfg

    savegoodautonfg New Member

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    Ok thank you very much, will be going through the test wiggle wiring tommorow.

    one other question,

    Where exactly does this black/white ground wire run to like where does it end?
     
    #73
  14. savegoodautonfg

    savegoodautonfg New Member

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    UPDATE!

    UPDATE:

    Just finished cleaning the hell outta the 10 pin white connector and i did the test light idea you had jritcher, and it seems like i might have an intermittent ground problem. It looks like when i wiggle the wires a certian way the test light does flash. i took the tape and the wire loom off and inspected the wires and from what i can see all looks good. its very strange. i then put everything back 2gether and start the car up and played with the wires while it was running and you could hear a few times the car idle flucuated a bit and made some noises.

    This part of the connector (wiring) does'nt seem to be the problem, it's seems like its the part that connects to the picture below:

    [​IMG]

    Lemme know jrithcher. thanks buddy.
     
    #74
  15. BigHairyMonkey

    BigHairyMonkey Founding Member

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    waow i pretty much have the EXACT same problem, just finished replacing my ACT ECT & 02's and a new IAC. Still idles higher than it should and stutters when engine is cold. Im almost certain its a vacuum leak somwhere. Im just waiting on someone to have a vac gauge for me to hook up.
     
    #75
  16. jrichker

    jrichker StangNet's favorite TOOL SN Certified Technician Founding Member

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    It is possible that the black/white wire has broken inside the insulation. Often wires will break inside the insulation
    and will only become evident when you pull on them and the wire stretches. You see the wire get longer as you pull
    on it, and you know that the copper does not stretch like plastic. In that case, you end up replacing the wire.

    Sometimes the crimp on pin will go bad from oil getting inside between the crimp part of the pin shell and the copper
    wire. Remove the wire from the plastic connector before doing anything else. Cleaning them with brake parts cleaner
    and then trying to solder them is the fix. Have some heat shrink tubing handy in case you melt some of the wire insulation.
     
    #76
  17. savegoodautonfg

    savegoodautonfg New Member

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    jrithker,

    the black/white wire is'nt the wire that is in the middle of the connector that the SIG-RTN is. that wire is gray with a red stripe?

    thanks for the reply, can you tell me how to get the wires out of the plastic connector?

    By crimp on pin do you mean the male part of the connector?
     
    #77
  18. savegoodautonfg

    savegoodautonfg New Member

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    Good luck. im pretty positive its my SIG-RTN wire i think so at least.
     
    #78
  19. jrichker

    jrichker StangNet's favorite TOOL SN Certified Technician Founding Member

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    I will have to spend some time looking at the connector and pin arrangement. On many ofthe connectors, you pry out an insert and then you can remove the pins. I haven't had a 10 pin taken apart in over18 months, so my memory isn't up to the give you good directions point.

    Don't jump on the same wagon as someone else just because it sounds the same. There was a lot of digging and testing to get to this point. Start your own post and dump the codes to see what you get.
     
    #79
  20. savegoodautonfg

    savegoodautonfg New Member

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    THANKS JRITCHKER
    anyone know how to take it apart?
     
    #80

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