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Thread: Borrow an idle motor?

  1. #1
    Senior Member BladeBronson's Avatar
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    Borrow an idle motor?

    I've been trying to diagnose a rough/high idle ever since I bought my car in October. I took it to Fremont Foreign Auto and Edwardo fixed a vacuum leak, adjusted the screws on the throttle, and adjusted the fuel mixture. It smells like it runs a little better and the idle problems seemed better, but not great (hovering in the 900 to 1100 range). Tonight, the car has been wildly fluctuating between 900 and 2000. I cleaned out the idle motor with brake cleaner and I looked inside while my girlfriend turned the car on and saw the valve close to 90%, which I think is correct. I just wonder if there's something else up with it.

    So, since these take just a couple minutes to pull off, I wondered if someone is nearby and could get together for an hour on the weekend so I can try your idle speed motor. I'm in San Leandro.

  2. #2
    Senior Member Bitsyncmaster's Avatar
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    So your trying to fix an idle hunting issue? In stock form, our engine idle is fixed at 775 RPM. Does yours idle at that RPM cold, hot or is the hunting so bad you can not tell what RPM it idles at?
    Dave M vin 03572
    http://dm-eng.weebly.com/

  3. #3
    Senior Member BladeBronson's Avatar
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    Thanks for the reply, Dave. I'll take a closer look Friday and will put together a video of the idle under different conditions (because I keep forgetting the specifics). I'm not sure if it would affect the idle, but my engine is a stage 2.

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    Quote Originally Posted by BladeBronson View Post
    I've been trying to diagnose a rough/high idle ever since I bought my car in October. I took it to Fremont Foreign Auto and Edwardo fixed a vacuum leak, adjusted the screws on the throttle, and adjusted the fuel mixture. It smells like it runs a little better and the idle problems seemed better, but not great (hovering in the 900 to 1100 range). Tonight, the car has been wildly fluctuating between 900 and 2000. I cleaned out the idle motor with brake cleaner and I looked inside while my girlfriend turned the car on and saw the valve close to 90%, which I think is correct. I just wonder if there's something else up with it.

    So, since these take just a couple minutes to pull off, I wondered if someone is nearby and could get together for an hour on the weekend so I can try your idle speed motor. I'm in San Leandro.
    Your idle motor sounds like it's functioning normally. In my experience stage two engines have a rougher idle than stock probably due to the cam profiles and advanced base timing. It sounds like resetting the CO again along with further testing is in order. Also ask one of the DMCH vendors what they set the base timing at and see if your's is correct.
    Rob

  5. #5
    President, DeLorean Industries
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    If this problem becomes worse and is not a base timing/CO adjustment concern the cams are the issue. We have consistently needed to replace stage II camshafts with excessive profile wear. If you find yourself needing valve adjustments regularly this is also the issue. Don't discount this or let the modifier of the engine tell you they haven't seen this. I've also forwarded this info to other independent vendors aware of the problem as well.

  6. #6
    Senior Member BladeBronson's Avatar
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    Okay, it sounds like I ought to buy a dwell meter and a timing light and see what I can find. Thanks guys.

  7. #7
    Senior Member BladeBronson's Avatar
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    I shot a video tonight of the idle problems and uploaded it here: https://www.youtube.com/watch?v=m0ZpiZ4GC0g. In the YouTube video description, I've added links to skip the video to interesting parts and noted what the conditions were. The most interesting bit is that the really high idle seems to dramatically drop when the headlights are turned off. However, there are occasions when the headlights are on and the car idles steady around 1,100.

    I bought a timing light and a dwell meter today. The timing light was defective and the dwell meter read "50" when set to 4 cylinder. I didn't adjust the mixture because the workshop manual says that the car should be idling normally before making adjustments.

  8. #8
    Senior Member Bitsyncmaster's Avatar
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    That bouncing tach and headlight changing does look like you have electrical problems. Have you posted what your voltages are reading at idle and higher RPM?

    Did your dwell hold steady after the engine warmed up? Normally the dwell will be swinging quite a bit up and down about 20 degrees or more.
    Last edited by Bitsyncmaster; 12-20-2015 at 04:20 AM.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  9. #9
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    I feel for you.

    I wouldn't believe your rpm gauge. I watched the whole video and throughout it sounded like your tach gauge was overstating the actual rpm. There's a ten second segment starting 20 seconds into the video where the engine sounds as if it's about to die, but tach gauge is indicating 1400 or so. Maybe it's the poor sound quality of my iPad but I could never reconcile the sound of the engine to what was shown on the tach gauge. I.e the engine always sounded lower rpm than what was indicated.

    Your battery voltage indicator reads very low like it isn't being charged. When you open the throttle it rises up to what I would think is a charging voltage but maybe your ignition circuit is struggling to provide a decent spark, due to the low system voltage, hence the rough running at idle. Only way to know that is make up some long cables connected to a multimeter and connect directly to the battery. As above, I would disregard the volt gauge in the binnacle.

    When you press on the gas pedal it runs miles better. My hunch is that is because when the throttle spool moves off the idlespeed switch the vacuum solenoid moves to send vacuum ignition advance to the distributor. So when you press the gas pedal and the microswitch is released suddenly the engine gets the full load of vac advance, 20 degrees, and runs much better. Suggests to me your basic ignition advance is too retarded.

    No idea about at the weird breathing sound right at the end of the video. I can't tell if it's fuel in the distributor causing that or just air through the intake.

    Don't worry, it'll be something(s) simple and silly, and when it purrs you'll be a happy man :-)

  10. #10
    Senior Member BladeBronson's Avatar
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    I checked the voltages today. The battery is 12.12 volts with the car off, just about the same at idle and just shy of 14 at 2,000 RPM. I also checked the voltage at the alternator and it's the same as at the battery. The alternator has a SpecialTAuto sticker on it and the belt is tight.

    I tested the RPM using an automotive multimeter at the coil wire. The RPM was consistent with what the binnacle tachometer displays.

    Last night when I was checking the dwell, I used the automotive multimeter with the positive lead on the orange wire running to the diagnostic port and grounded to the engine. It held at 50 the whole time.

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