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Thread: High Idle When Warm

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    Senior Member JRNY13's Avatar
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    High Idle When Warm

    My car idles fine when cold. However when it warms up the idle sits just below 1000rpms consistently. Snapping the throttle does nothing. Is this a vacuum issue? A vacuum leak would be present on a cold engine as well wouldn't it? Would getting vacuum on the ignition distributor cause a slightly high idle? If my decel springs were the culprit, wouldn't I get a high idle as soon as I pressed the throttle?

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    Quote Originally Posted by JRNY13 View Post
    My car idles fine when cold. However when it warms up the idle sits just below 1000rpms consistently. Snapping the throttle does nothing. Is this a vacuum issue? A vacuum leak would be present on a cold engine as well wouldn't it? Would getting vacuum on the ignition distributor cause a slightly high idle? If my decel springs were the culprit, wouldn't I get a high idle as soon as I pressed the throttle?
    Verify the idle motor is running when you are at idle. Vacuum leaks will reduce the ability of the idle motor to control the idle. Make sure the vacuum hoses for the vacuum advance are correctly hooked up and not leaking. The decel springs should be checked.
    David Teitelbaum

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    Check to see that all three of those brass screws just behind the W-pipe and threaded in all the way and tight. Their design purpose was to act as bypasses for air around the butterfly valves, but they were deemed unnecessary to be open at all with the engine set-up in our cars. If they are opened slightly, they will in effect create an offset from the normal design idle speed of 775 RPM to something slightly higher (depending on how far open they are and which one, or ones, of the three are open). You can see a good diagram explanation of how that air pathway works in the workshop manual.


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    Senior Member Bitsyncmaster's Avatar
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    Yes ignition advance on at idle will increase the RPM if your idle system can not compensate.

    My car had the same problem and it was the springs on the deceleration valves were bad. You can see your deceleration valves when you remove the W pipe. If the spacing on the springs is not even then your springs are bad.
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  5. #5
    Senior Member JRNY13's Avatar
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    Quote Originally Posted by Bitsyncmaster View Post
    Yes ignition advance on at idle will increase the RPM if your idle system can not compensate.

    My car had the same problem and it was the springs on the deceleration valves were bad. You can see your deceleration valves when you remove the W pipe. If the spacing on the springs is not even then your springs are bad.
    How would I go about replacing them if they're bad? Is this a part that is even sold?

  6. #6
    Senior Member Bitsyncmaster's Avatar
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    Quote Originally Posted by JRNY13 View Post
    How would I go about replacing them if they're bad? Is this a part that is even sold?
    I just got another used throttle assembly. I guess you could find some springs but you would need to test and calibrate the unit. I would guess they open around 20 inches/Hg
    Dave M vin 03572
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    Quote Originally Posted by Bitsyncmaster View Post
    I just got another used throttle assembly. I guess you could find some springs but you would need to test and calibrate the unit. I would guess they open around 20 inches/Hg
    Not a critical setting but they should be closed at idle. You can use the springs from old pens, cut them shorter.
    David Teitelbaum

  8. #8
    Senior Member Bitsyncmaster's Avatar
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    Quote Originally Posted by David T View Post
    Not a critical setting but they should be closed at idle. You can use the springs from old pens, cut them shorter.
    Have you used springs from old pens?

    I think it is critical for the calibration. You get 15 to 16 inches/Hg at idle so you just want them to open when you take your foot off the gas.
    Dave M vin 03572
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    Quote Originally Posted by Jonathan View Post
    Check to see that all three of those brass screws just behind the W-pipe and threaded in all the way and tight
    They most definitely should not be tight. They are shear screws and the heads will snap off if you tighten them up, leaving you SOL if you need to adjust them.
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    Quote Originally Posted by MikeWard View Post
    They most definitely should not be tight. They are shear screws and the heads will snap off if you tighten them up, leaving you SOL if you need to adjust them.
    Snug? Is snug a better choice of words? I hadn't meant to imply them being torqued, but rather not loose. If they were valves, I'd have said closed as opposed to open.

    Out of curiosity, when would you want to adjust these screws anyway? Page D:01:13 of the Workshop manual (fuel and emissions section) states that this single air adjusting screw and the two air balancing screws are not to be used on the DeLorean since we have an electronic idle speed control system. If they get adjusted, isn't that only trying to correct a problem elsewhere (per the design that is)?


    Sept. 81, auto, black interior

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