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Thread: Another high idle thread - how-to on butterfly plate springs?

  1. #21
    Administrator Ron's Avatar
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    No, heat expansion can make some vacuum leaks come and go.

    ======

    Uggg, the symptoms are changing a lot...

    Maybe take the throttle linkage loose, let it warm up and try it.
    If it does't stay high after several tries, it's probably the linkage.

  2. #22
    My friends think I'm nuts jawn101's Avatar
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    Quote Originally Posted by Ron View Post
    No, heat expansion can make some vacuum leaks come and go.

    ======

    Uggg, the symptoms are changing a lot...

    Maybe take the throttle linkage loose, let it warm up and try it.
    If it does't stay high after several tries, it's probably the linkage.
    So, disconnect the quadrant arm and leave it running at idle for a while, without any throttle movement?
    Jon
    1981 DMC-12 #02100. July 1981. 5-speed, black, grooved w/flap.
    restoration log, March 2011 to present
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  3. #23
    Administrator Ron's Avatar
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    Yes. And give it a good chance to raise on its own. If it don't, raise it with the arm and see if that does it. (Anything to get something consistent going on).

  4. #24
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    If you notice that you think you have vacuum leaks dependent on whether the car is hot or cold you need to investigate all of the vacuum systems. Some of them operate differently hot and cold. First do a visual inspection for routing and disconnected hoses. See if they are hard and brittle. Look for cracks. Make sure everything is hooked up and working. Look up Service Bulletins ST-18-10/81 and ST-32-12/81. It really matters how the vacuum advance solenoid is hooked up so check it carefully. Make sure it clicks. The quadrant link is a lefty-righty threaded rod. It can be very precisely adjusted in place but only if it is not worn. If it is worn, adjust it so it pushes the throttle arm to idle. You will have a bit of extra play when you step on the gas pedal but it will always go to idle. If you try to take the quadrant link out remember it has those tiny little clips like the struts do that MUST be removed first! To adjust it you just loosen the jam nuts and turn the rod.
    Last edited by David T; 11-14-2019 at 10:57 PM.
    David Teitelbaum

  5. #25
    My friends think I'm nuts jawn101's Avatar
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    Quote Originally Posted by David T View Post
    If you notice that you think you have vacuum leaks dependent on whether the car is hot or cold you need to investigate all of the vacuum systems. Some of them operate differently hot and cold. First do a visual inspection for routing and disconnected hoses. See if they are hard and brittle. Look for cracks. Make sure everything is hooked up and working. Look up Service Bulletins ST-18-10/81 and ST-32-12/81. It really matters how the vacuum advance solenoid is hooked up so check it carefully. Make sure it clicks. The quadrant link is a lefty-righty threaded rod. It can be very precisely adjusted in place but only if it is not worn. If it is worn, adjust it so it pushes the throttle arm to idle. You will have a bit of extra play when you step on the gas pedal but it will always go to idle. If you try to take the quadrant link out remember it has those tiny little clips like the struts do that MUST be removed first! To adjust it you just loosen the jam nuts and turn the rod.
    All good tips. Will verify the vacuum routing is right from the thermal switch in the valley, everything on the top end is visibly correct. All the hoses are new silicone, nothing brittle or cracked.

    Curious, how can I verify the vacuum solenoid is clicking? It is visibly connected right, electrical and vacuum. The electrical connection tests good, but if there's a way to feel/tell if it's actually engaging and not burned out internally that would be valuable. What's the test for that look like?
    Jon
    1981 DMC-12 #02100. July 1981. 5-speed, black, grooved w/flap.
    restoration log, March 2011 to present
    full and detailed photo restoration log

  6. #26
    Administrator Ron's Avatar
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    Pull the hose off of the distributor and feel it for vacuum.
    First, there should be no vacuum on the hose when the engine is cold. If there is, the valve or connection(s) in the VOD has a problem.

    Once the engine is warm:
    There should be no vacuum on the hose at idle.
    There should be vacuum on the hose when you raise the RPM.

    You can do also this with a timing light, but you have to allow for the distributor adding advance mechanically (hot or cold).

  7. #27
    My friends think I'm nuts jawn101's Avatar
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    Quote Originally Posted by Ron View Post
    Pull the hose off of the distributor and feel it for vacuum.
    First, there should be no vacuum on the hose when the engine is cold. If there is, the valve or connection(s) in the VOD has a problem.

    Once the engine is warm:
    There should be no vacuum on the hose at idle.
    There should be vacuum on the hose when you raise the RPM.

    You can do also this with a timing light, but you have to allow for the distributor adding advance mechanically (hot or cold).
    I think I may have made a mistake in my test protocol here, so the engine is cooling down and I will try again in a few hours. Here's what I did/observed:

    1. Disconnected quadrant arm from throttle spool, left it hanging
    2. Started engine, cold having sat overnight - idle at about 775
    3. Removed vacuum hose from solenoid to distributor, at the distributor end and felt it for vacuum. None there.
    4. Let the motor warm up for about 10 minutes
    5. Observed that the idle did in fact raise slightly, to about 1000 even with the quadrant arm disconnected
    6. Pressed on the upper idle screw (the one that actuates the idle microswitch) - idle dropped some
    7. Pulled the vacuum hose from the distributor again, still no vacuum there
    8. Decided to check the hose inbound to the solenoid from the thermal switch in the valley - plenty of vacuum (at idle, engine now warm)

    What I didn't test was:
    1. Did vacuum manifest on the output air line from the solenoid, with the RPMs raised
    2. Was there vacuum on the hose leading from the valley to the solenoid when the motor was cold (testing switch/routing)

    At this point I'm anticipating that when I re-do the test, I will find that the vacuum behavior between the switch in the valley and the solenoid/distributor is as expected, and the issue is actually to do with adjustment of those set screws for the microswitch/pivot point. I've never, ever touched those and I believe I recall that conventional wisdom was that you shouldn't. But I feel like if I back the lower one off a bit to move the fulcrum just a hair, then pick up the slack in the quadrant arm, it might resolve all of this.
    Jon
    1981 DMC-12 #02100. July 1981. 5-speed, black, grooved w/flap.
    restoration log, March 2011 to present
    full and detailed photo restoration log

  8. #28
    My friends think I'm nuts jawn101's Avatar
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    Another high idle thread - how-to on butterfly plate springs?

    Ok, so... there is vacuum to the center post of the vacuum solenoid, even at cold idle. That’s the hose that comes directly from the thermal switch.

    Does this mean something is hooked up backwards in the valley? I can swap the hoses that go to the solenoid and WUR, there’s enough slack to give that a try without opening the intake. Should I do that?

    I also confirmed that there is no vacuum coming from the solenoid to the distributor at idle, but when I open the throttle the vacuum there is strong.
    Last edited by jawn101; 11-15-2019 at 05:16 PM.
    Jon
    1981 DMC-12 #02100. July 1981. 5-speed, black, grooved w/flap.
    restoration log, March 2011 to present
    full and detailed photo restoration log

  9. #29
    Administrator Ron's Avatar
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    Quote Originally Posted by jawn101 View Post
    Ok, so... there is vacuum to the center post of the vacuum solenoid, even at cold idle. That’s the hose that comes directly from the thermal switch.

    Does this mean something is hooked up backwards in the valley?
    It means that the the thermal vacuum switch is failing to switch vacuum to the WUR/CPR when it is cold.

    Quote Originally Posted by jawn101 View Post
    ..., but when I open the throttle the vacuum there is strong.
    This and symptoms 1, 7, 8 means the solenoid and switch should operate correctly when the valve is fixed. Confirm it is bad by checking to see if the WUR/CPR has vacuum when it is dead cold.
    If it don't have vacuum cold the valve is not doing its job. If it does, the valve might be sending vacuum to both all the time...

    Sounds like you need to adjust the linkage to make it favor shut (as mentioned above) and maybe test the microswitch using a tiny screwdriver w/o disturbing anything else while it is revved up on its own.
    And connect a spare hose to the distributor and draw on it to making sure it is holding vacuum and not the source of a leak.

  10. #30
    My friends think I'm nuts jawn101's Avatar
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    Quote Originally Posted by Ron View Post
    It means that the the thermal vacuum switch is failing to switch vacuum to the WUR/CPR when it is cold.


    This and symptoms 1, 7, 8 means the solenoid and switch should operate correctly when the valve is fixed. Confirm it is bad by checking to see if the WUR/CPR has vacuum when it is dead cold.
    If it don't have vacuum cold the valve is not doing its job. If it does, the valve might be sending vacuum to both all the time...

    Sounds like you need to adjust the linkage to make it favor shut (as mentioned above) and maybe test the microswitch using a tiny screwdriver w/o disturbing anything else while it is revved up on its own.
    And connect a spare hose to the distributor and draw on it to making sure it is holding vacuum and not the source of a leak.
    Roger that, I will test the vacuum again when the car has sat for a few more hours to cool. If there is *not* vacuum at the WUR when cold, is it possible the hoses were simply placed on the thermal switch backwards? I did a valley job to put new water hoses in a few weeks ago and a lot of these idle issues have cropped up or become more obvious since then. If that's the case, my test of just swapping the hose to the center nipple on the solenoid and the hose feeding the plastic T on the WUR should be helpful - and a possible temporary fix?

    Will work on the throttle adjustments only after I rule out these other factors.

    Thanks as always Ron!
    Jon
    1981 DMC-12 #02100. July 1981. 5-speed, black, grooved w/flap.
    restoration log, March 2011 to present
    full and detailed photo restoration log

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