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Thread: Help with a high idle....

  1. #1
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    Help with a high idle....

    Hi all-first off, let me first say I have tried to use the search function, as well as read through the manual, before posting here. I've made some progress, but still haven't solved my issue.

    I took my DMC out 2 weeks ago. Ended up driving on the highway for about 30 minutes, which I usually don't do. About midway thru that drive, the idle started pegging around 1700-1800RPM. It's been this way since. Upon startup, it will waffle around the ideal 750-ish range for about 5 seconds, then it floats slowly up to 1700-ish, and stays there.

    I checked my electrical connections, and everything seems securely seated around the idle speed motor(there's a loose harness at the near side of the intake, but I see no female counterpart to it). I adjusted the idle speed screw all the way out, so the striker very securely depresses the switch when closed-no change. (part of my problem is that the manual doesn't clearly denote the parts of the idle speed motor with names, so my language here is lacking, sorry!). I read in one thread to check for 12V at a point, but it wasn't clear to me which test point I should see 12V.

    Any further pointers would be hugely appreciated. Thanks!

  2. #2
    Not a DeLorean Guru
    Join Date:  May 2011

    Location:  Rochester, NY

    Posts:    1,715

    My VIN:    01049

    Does the idle change if you press in on the microswitch manually with, say, your finger?
    -Mike
    1981 DeLorean, heads/cams/exhaust, EFI
    1999 Corvette, heads/cam/exhaust, 440 BHP
    2005 Elise, stock
    2016 Chevy Cruze

  3. #3
    Senior Member Bitsyncmaster's Avatar
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    Location:  Leonardtown, MD

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    My VIN:    03572

    You need to back out the idle switch screw if it's bottoming out on the switch. That would still be holding the throttle open.

    But if this happened suddenly, it's probably not that adjustment causing the problem.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  4. #4
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    Quote Originally Posted by opethmike View Post
    Does the idle change if you press in on the microswitch manually with, say, your finger?
    Is the microswitch the vertical flat metal plate, about 2 sq cm, with the little tiny trigger underneath it? if so, yes-i tried depressing it, and it does nothing.

  5. #5
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    Quote Originally Posted by Bitsyncmaster View Post
    You need to back out the idle switch screw if it's bottoming out on the switch. That would still be holding the throttle open.

    But if this happened suddenly, it's probably not that adjustment causing the problem.
    agreed-i can say with surety this screw did not change position; i can tell from the slight corrosion around it. I'll back that screw back in until it just barely triggers the idle switch.

  6. #6
    Senior Member Jonathan's Avatar
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    Quote Originally Posted by rjd2 View Post
    Is the microswitch the vertical flat metal plate, about 2 sq cm, with the little tiny trigger underneath it? if so, yes-i tried depressing it, and it does nothing.
    Yes, sounds like you've found the right one.

    This is it on the parts webpage: http://store.delorean.com/p-6743-microswitch.aspx

    It shows the wiring connections on the back and not the front little trigger you described that gets depressed.

    Here is a photo of the switch on my own car:

    Idle microswitch.jpg

    ~~~

    You mentioned a connector, or portion of wiring harness, that isn't connected anywhere and you couldn't find the female end that it might go with. It may be a connector that isn't used on the car or it could be something important. When I hear a car's idle sits up as high as you've described, it can sometimes mean the connection to one of the thermal sensors under the intake got loose. If that happens, the engine will sit just about exactly at 2,000 RPM and depressing the idle microswitch won't change a thing. I suspect the connector you found is the one along the firewall and isn't used though. If you can post a photo of this, that would help confirm.
    One damn minute Admiral...


  7. #7
    Senior Member Jonathan's Avatar
    Join Date:  Jun 2011

    Location:  The Great White North Korea

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    Quote Originally Posted by rjd2 View Post
    Is the microswitch the vertical flat metal plate, about 2 sq cm, with the little tiny trigger underneath it? if so, yes-i tried depressing it, and it does nothing.
    Quote Originally Posted by rjd2 View Post
    agreed-i can say with surety this screw did not change position; i can tell from the slight corrosion around it. I'll back that screw back in until it just barely triggers the idle switch.
    It's conceivable that the electrical connections on the back of the idle microswitch aren't making good contact. That would leave you with the impression that depressing the trigger on the front is having no impact, because the switch isn't well connected electrically.

    You can pull the two connections off the back of the switch and inspect and then reconnect ensuring they are nice and snug.
    One damn minute Admiral...


  8. #8
    Not a DeLorean Guru
    Join Date:  May 2011

    Location:  Rochester, NY

    Posts:    1,715

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    Quote Originally Posted by Jonathan View Post
    It's conceivable that the electrical connections on the back of the idle microswitch aren't making good contact. That would leave you with the impression that depressing the trigger on the front is having no impact, because the switch isn't well connected electrically.

    You can pull the two connections off the back of the switch and inspect and then reconnect ensuring they are nice and snug.
    +1

    With the age of these cars, it is always a good idea to check connection quality.
    -Mike
    1981 DeLorean, heads/cams/exhaust, EFI
    1999 Corvette, heads/cam/exhaust, 440 BHP
    2005 Elise, stock
    2016 Chevy Cruze

  9. #9
    Senior Member
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    great, I really appreciat that you prepared yourself and used the search :-)

    I'd try to check first if the problem is electrical or mechanical.

    1. when the idle is high - pull the connector of the idle motor
    2. with 2 wires you connect the center pin of the idle motor to +12V
    and then touch one of the outer two pins with Ground - just for a second.

    in one position the idle should go up (idle motor fully open)

    in the other the idle should go down (idle motor fully closed)

    please report how your car is behaving.


    The ECU could be bad, but let's see first what your car does.

  10. #10
    Member
    Join Date:  Mar 2016

    Posts:    33

    thanks everyone!

    attached is the image of the loose harness. I had to run the car to move it into position, so i'm gonna let the manifold and such cool off a bit before testing the backside of the idle microswitch; I'll report back soon.

    edit: sorry, the photo flipped upside down when i uploaded it for some reason...
    Attached Images

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