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Idle low when ac is on IAC motor does not move

Discussion in 'EEK! - Every Extended-K Car' started by neon98rt, Jun 17, 2017.

  1. neon98rt

    neon98rt Member

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    3.0 90 lebaron
    I noticed my idle is low when the ac is on. The car does not stall but the voltage drops below 12v since the idle is low. As soon as you move its back to 14.4 v.
    When the car is at idle i can unplug the IAC motor and nothing happens . I bought a new motor and the plunger thing was not extended all the way and the car rev at 4grand. I took the new one out and put the old one back in that seems to be fully extended. I unplugged the old one and let the new one hang from the wire. It never moved.
    I am just glad my old one is stuck closed or my car would be at full idle.
    What makes the motor move and what needs to be replaced. Sadly i dont have a TPS spare since 1990 was a one year only tps.
    I think the reason my car even idles is i turned that do not turn screw a long time ago.
     
  2. Bob Lincoln

    Bob Lincoln "CHECK FAULT CODES" Level 2 Supporter

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    I believe when you install the AIS, you need to turn the key on and leave it for something like several seconds, or turn it on and off without starting, to set the initial position. The new one was not fully extended, which is good, as it is not supposed to be when you install it. I would put it back in. Someone can give the initial procedure.

    As to the screw that sets air flow, if you messed with that, the whole idle situation is messed up. The official procedure for correcting/setting it involves flowing propane into a vacuum port at a certain rate while setting the idle with the screw. But there is a cheater procedure that, again, someone here will know.

    What speed does it idle at with accessories off, and with A/C on?
     
  3. ImperialCrown

    ImperialCrown Moderator Level III Supporter

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    It is a feedback/stepper motor.
    Idle (at https://speeduino.com/wiki/index.php/Idle )
    With the IAC motor plugged in and removed from the throttle body, it should cycle out, then in when moving the ignition key from off to run. This sets the plunger to a fast idle when initially starting the car. The idle will then settle back to a curb idle. This is called idle-flare when starting the car. If it doesn't do that, there is a problem.
    On the 4-wires to the IAC, 2 are for IAC position feedback to the PCM (to let it know how many 'steps' the motor is in or out). The other 2 wires are to drive the motor to move the plunger position in or out.
    Idle speed is an 'adaptive', which means that the PCM memorizes the position for correct idle. It can also change it as other conditions change.This adaptive gets lost during a battery disconnect or it can be reset with a scan tool.
    If the IAC does not respond and you have replaced the IAC, check all 4 wires for continuity to the PCM. If they are OK, it may be a PCM problem. If the motor drive wires have rubbed-through to ground, this can short the drivers in the PCM and the PCM will have to be replaced.
    There is an orifice (Miller tool # 6457) for metering the correct amount of air flow that goes in place of the PCV valve. The DRB then fully closes the IAC and 'minimum air' is set. Notice that I didn't call it idle speed, because it isn't. The tool and min-air procedure sets the reference of the throttle body at closed throttle. The PCM determines correct idle speed and timing.
    Miller Special Tools 6457 Fitting/Air Metering (at http://www.autotoolworld.com/Miller-Special-Tools-6457-FittingAir-Metering_p_156241.html )
     
  4. neon98rt

    neon98rt Member

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    I put the old IAC motor in the hole while i plugged in the new one for it to " step out " a bit . It moves back and forth like it should.
    I took the TB off and hooked a multi meter to the TPS and turned the screw until the reading was the lowest.
    Its good to know that the computer learns , I think mine needs more learning.
    With the new iac i noticed a higher idle at start up .
    I am still not impressed with how low it is with the AC on.
    I have a 52mm TB and i did notice when the mulit meter was on it that it reads 6 when fully closed is 4. I dont know how to lower it besides drilling out larger holes . I think the computer thinks the plate is open when its not and steps back the IAC. Anyone know the range for a tps?
     
  5. neon98rt

    neon98rt Member

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    What is your best guess for why the idle speed does not go up when the ac is on?
     
  6. ImperialCrown

    ImperialCrown Moderator Level III Supporter

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    A TPS should generally read around 0.65 volts at closed throttle. It will vary from car to car. There is no real spec.
    If the IAC plunger responds as it should, then I would suspect that there is an issue with the A/C? I have had over-charged, over-oiled and mechanical over-drag from failing compressors pull the idle speed too low only when the A/C is on.
    This happened to my Neon once where it could stall the engine when the A/C was turned on.
     
    Bob Lincoln likes this.
  7. neon98rt

    neon98rt Member

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    off it read .4 and on with closed butterfly it read around that .6. I guess i could take it off and see how my idle is. It will think it is truly closed. My worry is .6 or .7 is "open" to the computer and it thinks the car is going down the road so it backs off the IAC.
    I wonder if the IAC even moves when the AC is on and you are going down the road. Is it still stepping or just in standby for when you come to a stop?
     
  8. neon98rt

    neon98rt Member

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    What do i unscrew to let some AC stuff out... lol
     
  9. ImperialCrown

    ImperialCrown Moderator Level III Supporter

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    What are your A/C pressures at idle?
    Is the radiator cooling fan running with the A/C on? A very high discharge-side pressure can load the engine down.
    The IAC may help regulate the throttle when the A/C cycles on and off while driving.
     
  10. neon98rt

    neon98rt Member

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    The fan is running. Fan on its own does not lower idle 195 degree turn on.
    The dealership did the AC . I dont have gauges .
    So you let some out to correct the high discharge pressure? I really dont want a 150 dollar bill for a refill.
     
  11. Doug D

    Doug D Virginia Gentleman

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    By law AC freon cannot be simply discharged into the atmosphere. It must be recovered into a closed storage system by a licensed AC technician. Either way you'll need to have a technician check the pressures and recover any excess freon.
     
    Bob Lincoln likes this.
  12. ImperialCrown

    ImperialCrown Moderator Level III Supporter

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    Don't guess. If you don't know the pressure, don't arbitrarily discharge any pressure.
    I never said that it was definitely your problem, only something to consider as a possibility.
    A dealer should have given it an accurate fill, but that it an unknown right now.
     
    Bob Lincoln likes this.
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