Help with a high idle....

[rjd2]

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!

[opethmike]

Does the idle change if you press in on the microswitch manually with, say, your finger?

[Bitsyncmaster]

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.

[rjd2]

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.

[rjd2]

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.

[Jonathan]

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:

52253

~~~

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.

[Jonathan]

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.


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.

[opethmike]

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.

[Elvis]

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.

[rjd2]

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...

[Jonathan]

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...

That piece you show not plugged into anything is fine. It is for automatic transmission cars (assuming you have a manual trans car). If you had an auto, you would have a second, similar switch stacked on top of the one you see there connected to the white connector. They both get activated by pressing the gas pedal all the way to the floor, and then when the throttle spool rotates all the way around, it presses up against that metal flap and engages the switches. That's called the wide open throttle or full throttle switch. The one you have enriches the fuel mixture and the additional one on the automatic kicks it down one gear.

Anyway, back to the idle microswitch we were wondering about... you see that bright red plastic splice connector that is on the single wire going to your idle switch? That's been added after the fact by someone and could be part of your problem. See if you can follow what else might be spliced into it and also if it seems loose.

[rjd2]

ok, more info:52315

1) is this the microswitch? i don't want to lose anything in translation/assumption on my part. whatever this part is, if i manually depress it, the idle speed actually goes UP by about 300RPM or so.

2)as i have been hunting this problem, the standing idle speed has now risen to about 2300-2500.

3) with the engine off, i detached the cream harness that runs to the pictured switch here. if i run a DVM across the two pins, and manually depress the switch, at the 2Meg setting, switch depression throws the impedance to 0. I do not know if that is proper, but the switch is definitely not INactive entirely.

4)with the car running, detachment of the cream 2 pin harness has no effect on idle speed.

5) the two connections on the back of the plate that is depressed by the idle screw(is THAT what is considered the microswitch?), one a yellow wire and one a black/green wire, they seem snug-i checked them.

Elvis-I wanted to do your test, but I cannot find a 3 pin harness leading to the idle motor anywhere. The only detachable harness I'm finding is that cream colored 2 pin harness.

[rjd2]

ok! sorry for my ignorance, upon further research, the microswitch i previously posted an image of is the FULL THROTTLE switch. i now see that the idle speed microswitch is the larger one next to the air intake valve with two wires(black and black/green) leading to it.

attached is an image of a can-thing; the yellow wire that runs out of it, the joint is failing. i either need to take it apart and solder it, or replace it. what is that canister thing?

52318

lastly, the red junction point on the wires to the idle speed microswitch is just that-it's a non-solder junction; it basically taps into the green/black wire and provides a junction point for the yellow wire. it was on the car when i acquired it.

[opethmike]

The electrical connector to the idle speed motor is black. If you pull that off of the motor, there will be three pins.

[DMC-81]

ok! sorry for my ignorance, upon further research, the microswitch i previously posted an image of is the FULL THROTTLE switch. i now see that the idle speed microswitch is the larger one next to the air intake valve with two wires(black and black/green) leading to it.

attached is an image of a can-thing; the yellow wire that runs out of it, the joint is failing. i either need to take it apart and solder it, or replace it. what is that canister thing?

52318

lastly, the red junction point on the wires to the idle speed microswitch is just that-it's a non-solder junction; it basically taps into the green/black wire and provides a junction point for the yellow wire. it was on the car when i acquired it.

I believe the canister thing is the coil suppressor, 108561, http://store.delorean.com/p-6878-suppressor-coil.aspx
You can see it in the lower left of this picture:

52319

[rjd2]

I believe the canister thing is the coil suppressor, 108561, http://store.delorean.com/p-6878-suppressor-coil.aspx
You can see it in the lower left of this picture:

52319

thanks. the wire leading to the coil suppressor completely failed; i've ordered the part, and once in place, i'll continue tests and report back. thanks much all!

[Elvis]

That has nothing to do with your high idle.

[NckT]

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

[Elvis]

what means "^^^^" ?

[NckT]

what means "^^^^" ?

It's supposed to reference your post above, as in an upward arrow

[NckT]

As in my post above ^^^^

[Elvis]

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

[NckT]

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 :D

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 :D

[opethmike]

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.

:devil::devil::devil::devil::devil::devil::devil:: devil::devil::devil::devil:

[NckT]

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.

:devil::devil::devil::devil::devil::devil::devil:: devil::devil::devil::devil:

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

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

Oem stock/ modifications/ engine swaps, it's all good.

[rjd2]

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!

[Elvis]

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.

[NckT]

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?

[rjd2]

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!

[AugustneverEnds]

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.

[NckT]

The 'thermister' is physically located on the V coolant pipe under the inlet manifold.

To test it, just remove the white electrical connection from the idle ecu that has 4 wires on it.

Set your multi meter to resistance (0-100 k ohm) and connect the multi meter probes to the Black/Slate (grey colour) and the Black/Yellow cables (not the ecu itself)

You should get approx 12k ohm at engine warm temperature.

If you get open circuit then that's your problem. I.e. a wiring problem or connection problem.

Good luck

Nick

[Jonathan]

I added a thermister location photo here: http://dmctalk.org/showthread.php?10336-Assorted-helpful-technical-photos&p=222057&viewfull=1#post222057

[Elvis]

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.

thanks for the help!


I am wondering a bit - why would the speed drop after 1-2 seconds ?
The idle motors that I know stay in their position, they do not close by themselves.

I did not expect this answer.

The goal was to find out if the idle is to high because of a mechanical problem or
because of the ECU. I don't undestand why your car would be different.

If it's the ECU -it could be the thermistor or simply the power stage transistor that failed ( very common).

[rjd2]

It was suggested to "just tap" either the left or right pin to ground, so that's what I did. I just tapped a jumper wire very quicklyf from the left pin on the motor to ground; it raised the idle to ~1500 for about 2 seconds, and then it fell back to it's resting rate with the black idle speed harness DISconnected(~500 or so). If any of my testing methodolies are off here, please correct me! Thanks!


I am wondering a bit - why would the speed drop after 1-2 seconds ?
The idle motors that I know stay in their position, they do not close by themselves.

I did not expect this answer.

The goal was to find out if the idle is to high because of a mechanical problem or
because of the ECU. I don't undestand why your car would be different.

If it's the ECU -it could be the thermistor or simply the power stage transistor that failed ( very common).

[Bitsyncmaster]

It was suggested to "just tap" either the left or right pin to ground, so that's what I did. I just tapped a jumper wire very quicklyf from the left pin on the motor to ground; it raised the idle to ~1500 for about 2 seconds, and then it fell back to it's resting rate with the black idle speed harness DISconnected(~500 or so). If any of my testing methodolies are off here, please correct me! Thanks!

I wonder if your idle speed motor is installed backwards. Can you post a photo of it.

[rjd2]

Thanks. I just did this test; at resting temp, it read ~4.5k. After running the car for about one minute, it read ~2.4k. That sounds off, eh?


The 'thermister' is physically located on the V coolant pipe under the inlet manifold.

To test it, just remove the white electrical connection from the idle ecu that has 4 wires on it.

Set your multi meter to resistance (0-100 k ohm) and connect the multi meter probes to the Black/Slate (grey colour) and the Black/Yellow cables (not the ecu itself)

You should get approx 12k ohm at engine warm temperature.

If you get open circuit then that's your problem. I.e. a wiring problem or connection problem.

Good luck

Nick

[rjd2]

Also, I'm not sure if this matters, but in the attached pic, you will see a red wire with a fuse in line. The fuse socket was empty. With the car not running, or keys in, i seated a fuse, and the fuse blew immediately. Not sure what that means, if anything...52585

[Elvis]

tapping ground on one side fully opens the valve, on the other side fully closes the valve.

so simple.



and that fuseholder is from the power antenna