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Thread: Help with a high idle....

  1. #21
    Member NckT's Avatar
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    Location:  Yorkshire UK

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    My VIN:    No. 4068

    As in my post above ^^^^
    I say Sir, I must be mad, one loves fixing K-Jet !

    Make sure there's plenty in the tank for the weekend chaps....

  2. #22
    Senior Member
    Join Date:  May 2011

    Posts:    509

    wow, and you love fixing K-Jet ?

    no carbs ?
    no EFI ?

    instead reading manuals and fixing classic cars ?


    you are unusual :-D



    Where ist the Facbeook- I like - button ? :-P

  3. #23
    Member NckT's Avatar
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    Location:  Yorkshire UK

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    My VIN:    No. 4068

    Quote Originally Posted by Elvis View Post
    wow, and you love fixing K-Jet ?

    no carbs ?
    no EFI ?

    instead reading manuals and fixing classic cars ?


    you are unusual :-D



    Where ist the Facbeook- I like - button ? :-P
    My friends tell me I'm 'special', but I'm taking that as a plus point

    I fix carbs and diagnose efi on modern cars too as a hobby, but I like k jet, especially in the D. I've fixed a few other Deloreans in my time since I've had my own since 2003.

    Btw, I'm not on Facebook or social media either (other than my friends/ other owners on "wattsapp"), that must make me double unusual
    I say Sir, I must be mad, one loves fixing K-Jet !

    Make sure there's plenty in the tank for the weekend chaps....

  4. #24
    Not a DeLorean Guru
    Join Date:  May 2011

    Location:  Rochester, NY

    Posts:    1,725

    My VIN:    01049

    Quote Originally Posted by Elvis View Post
    wow, and you love fixing K-Jet ?

    no carbs ?
    no EFI ?

    instead reading manuals and fixing classic cars ?


    you are unusual :-D



    Where ist the Facbeook- I like - button ? :-P

    So I shouldn't mention that I EFI converted my PRV, and that I am currently working on swapping in an LS4 in place of the PRV? Definitely shouldn't mention that.

    -Mike
    1981 DeLorean, heads/cams/exhaust, EFI
    1999 Corvette, heads/cam/exhaust, 440 BHP
    2005 Elise, stock
    2016 Chevy Cruze

  5. #25
    Member NckT's Avatar
    Join Date:  Jun 2011

    Location:  Yorkshire UK

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    My VIN:    No. 4068

    Quote Originally Posted by opethmike View Post
    So I shouldn't mention that I EFI converted my PRV, and that I am currently working on swapping in an LS4 in place of the PRV? Definitely shouldn't mention that.

    It's your car fella, you can do what you like with it

    We've got Deloreans with modded exhausts, Volvo conversions etc in the Uk.

    Oem stock/ modifications/ engine swaps, it's all good.
    I say Sir, I must be mad, one loves fixing K-Jet !

    Make sure there's plenty in the tank for the weekend chaps....

  6. #26
    Member
    Join Date:  Mar 2016

    Posts:    38

    Alright, had a big work project for a while, but that's wrapped and now I can focus on the important things in life like idle issues on a 35yr old car!

    Upon further diagnosis, I have some new insights:

    1-one hose clamp on the far side of the idle speed motor was loose; I tightened and reseated all the hose clamps, and as best I can tell, they are all seated thoroughly. This brought the high idle down from ~2400 to ~1700, so it helped, but didn't solve the problem.

    2-I've found that if I pull the black 3 pin electrical harness to the top of the idle speed motor while the car is running, the idle drops down to exactly where I want it, ~800. If I reseat it, it jumps to ~1700, consistently.

    I haven't found an elegant way to unseat the 3 pin harness, and jumper +12V and ground to the idle motor pins, but that's my next diagnostic test. Any further ideas on the reseating/unseating motor harness test would be great-thanks!

  7. #27
    Senior Member
    Join Date:  May 2011

    Posts:    509

    what mor details do you need ?

    I described it weeks ago.
    It's a few second test and then you know if it's mechanical or electrical.

  8. #28
    Member NckT's Avatar
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    Location:  Yorkshire UK

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    Quote Originally Posted by NckT View Post
    As Elvis said ^^^^

    That capacitor is an attempt to try and reduce arcing on the switch contacts to reduce wear etc.

    You'd be better off trying to do continuity tests from the idke ecu to the various ends to prove the wiring (via the bulkhead connectors). You can't do the continuity to the microswitch though as this goes via the anti-back feed diode, but you could use the diode function on a multi meter and test this at the ecu and switch end wiring.

    Diagnostics are best but to save time, typical causes of High idle are (in no particular order):

    Vacuum leaks (idle motor brass pipe to venturi O ring not in place/ poor seal)

    Upper throttle 'hammer' not making contact on the microswitch/ not adjusted correct

    Bad connection/ open circuit thermister (check for resistance at the ecu multi plug disconnected from the ecu)

    Stuck/ sticking idle control valve

    Shorted winding in idle control valve that causes one of the ecu's switching transistor to fail (ecu can be fixed for 2 or so)

    Run on Air admittance (Poppet) emission valves on the throttle disc spring failure

    Poor adjustment of the accelerator cable

    Sticking throttle spool/ bad link rod adjustment/ mechanical issue.

    Good luck
    Have you done all of the above tests on this?
    I say Sir, I must be mad, one loves fixing K-Jet !

    Make sure there's plenty in the tank for the weekend chaps....

  9. #29
    Member
    Join Date:  Mar 2016

    Posts:    38

    Quote Originally Posted by Elvis View Post
    what mor details do you need ?

    I described it weeks ago.
    It's a few second test and then you know if it's mechanical or electrical.
    yes, thanks for that test. If I'm understanding correctly, I pull the 3 pin black electrical connector to the idle speed motor, bridge the middle pin(+12V), and then tap either of the left or right pins to ground. My alligator clip method is a bit janky, but I was able to do this and at least bridge the left pin to ground. It goosed the idle speed up to about 1500-ish for about 1-2 seconds, then it fell back to the ~500-ish range that it idles at with the motor disconnected. I will try to test the right pin tapped to ground, and see what it does.

    Yes, I ran thru the checklist there. Everything seems to be in order, as best I can tell, save for these two items:

    -thermister: i can't find it. (sorry, as you can see, I'm green on the DMC-12.) I've got the diagram out, and I'll stare at it further, and find it next.

    -the copper pipe that connects to the FAR end of the idle speed motor; this looks to connect underneath near the distributor; I can't find that connection to check the hose clamp's security. the end that connects to the hose out of the far side of the idle speed motor was loose; it feels like it may have some play, so possibly the other end of that copper pipe needs a hose clamp secured?

    thanks for the help!

  10. #30
    TGTF (Too Greek to Function) AugustneverEnds's Avatar
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    Location:  Syracuse, NY area

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    Club(s):   (DMA)

    The thermistor is screwed into the coolant distribution pipe (the Y-pipe) underneath the intake manifold in the VOD (valley of death). Not easy to see with the intake in place.

    The copper pipe that runs from the idle speed motor to the fuel mix unit (aka Pipe of Agony) needs to be seated securely or it can cause idle issues. Remove the air filter housing and push open the air deflector plate and shine a flashlight in there and verify if the end of the copper tube is securely in there.
    Nick A.
    Νικος Αυγουστινατου

    1988 BMW 325iS
    1982 DeLorean DMC-12

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