RPM, Hunting, Idle problems

[Bitsyncmaster]

I just remembered I was working with an owner with idle problems holding the correct RPM. I finally suggested to try turning his idle motor around (the wrong way) and that solved his problem. My thought of doing that is the idle motor is sticking. Mounted the correct way the engine vacuum pulls the seal against the housing. Mounted backwards pulls it off the housing.

It would be interesting if other owners try this and hear their results. Real easy to do.

[JohnZ]

You mean with the notorious "arrow" pointing towards the rear of the car instead of the front?

I've always had severe hunting problems at idle (700~1500 rpms very often, no matter the temperature): I'm about to properly seal the pipe of agony hole, cause it was always "rattling"... The idle speed motor is new, I have to dedicate myself into it, because I always neglected this issue!

But would turning the speed motor backward invalidate it's function?

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[Bitsyncmaster]

You mean with the notorious "arrow" pointing towards the rear of the car instead of the front?

I've always had severe hunting problems at idle (700~1500 rpms very often, no matter the temperature): I'm about to properly seal the pipe of agony hole, cause it was always "rattling"... The idle speed motor is new, I have to dedicate myself into it, because I always neglected this issue!

But would turning the speed motor backward invalidate it's function?

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Yes reverse it and test if that cures your hunting. It still will maintain constant idle RPM. The idle motors have very little torque to overcome any friction.

[JohnZ]

I'll definitely try that, for knowledge's sake! But I don't really think that this would be the right way to solve the problem, over all.... (I have to seal that freaking pipe of pain)

I mean that if the airflow was designed to be managed in a certain way, why would we want to tamper with that?

Aside from these considerations, I'll try that for sure!

I hope I won't be damaging anything :)

[JohnZ]

Well I was able to perform the job during lunch break. I swapped the orientation of the idle speed motor, but literally nothing changed in my idle: still going from 700 to 1400 rpms.

But this gave me something to think about: approximately 1 year ago I installed a brand new Idle speed motor that I bought from DeLoreango. I installed it as per instructions: with the arrow pointing to the rear of the car. Now I've looked into it and I found sources that tell you to install it with the arrow pointing towards the front of the car. I have no clue about this matter :)

Now my idle speed motor has the arrow pointing towards the front of the car. Is it right? Should I turn it backwards once again? It literally has no impact on the idle rpms, so...

:)




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[Bitsyncmaster]

Now my idle speed motor has the arrow pointing towards the front of the car. Is it right? Should I turn it backwards once again? It literally has no impact on the idle rpms, so...
:)

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Not sure which way the arrow should point but all the cars I've seen, the connector is closest to the front of the car. When does your engine hunt? If it's right after the lambda goes active (about 3 minuets after cold start), I've found that hunting is caused by the lambda ECU.

[JohnZ]

Well... always! And it was always that way! I sort of got used to, and I fthink it's a feature that you can make a joke or two about it, when talking about the Delorean! But I've always wanted to know what's causing that. I checked the vacuum routing and everything seems fine, except for the play when I wiggle the pipe of pain. As I said I will soon check the oring on the mixture unit because I feel it's too loose. Maybe it's just that :)

There are certain instances in which the car idles perfectly, but they are scarce... sometimes when I fire it up it stays that way for one minute or so, than it starts to hunt. Earlier, when I tried the ISM swap, as soon as I fired it up it started to hunt... so I cannot identify a coherent behaviour.

I'll try to keep an eye on that, to see if I can pinpoint certain conditions where the engine doesn't hunt and get back to you!

[dn010]

It helps to clean the idle motor with brake clean or carb cleaner then spray some PB blaster or whatever your favorite lubricant is into it to get it moving smoothly. I eventually went to the smaller idle speed motor from the B280F engine (Volvo 780 Bertone).

I can't help with your idle issue but I can suggest to take a look at, and clean the bulkhead connectors. Back when I ran K-Jet I had all kinds of issues until I cleaned and tightened those connectors. Sometimes just wiggling one of the connectors would result in the engine quitting, or running perfect for me.

[JohnZ]

I'll give it a go! As I said the idle Speed motor from DeLoreango is brand new, so I don't think it needs cleaning.... Now I'm bugged about the orientation of the thing!

And also I'm baffled at the fact that one way or another it doesn't really affects the idle behavior!

What's wrong with these cars? I hate them! ...And I also love them a lot :)

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[iflights]

According to the web page for the DeloreanGo ISM, arrow should face license plate.

https://www.deloreango.com/us/idle-speed-control-valve-regulator-motor.html

[JohnZ]

According to the web page for the DeloreanGo ISM, arrow should face license plate.

https://www.deloreango.com/us/idle-speed-control-valve-regulator-motor.html

...but according to this discussion (page 11):

http://www.deloreans.co.uk/forum/archive/index.php?thread-5860-11.html

it should point towards the front, aka the pipe of agony.

[dn010]

Back when I had idle problems I tried it both ways and it did not change my idle issue. Aside from cleaning connectors and replacing fuel components, the only thing that worked at the end was a new idle ECU.






And also I'm baffled at the fact that one way or another it doesn't really affects the idle behavior!

What's wrong with these cars? I hate them! ...And I also love them a lot :)

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I'd clean bulkhead connects. Also check all the other electrical connectors, my ISM once time had a wire broken off under the rubber boot that could not be seen without pulling the boot back. If all else fails, I'd try to swap out with a known good idle ECU.

[Bitsyncmaster]

...but according to this discussion (page 11):

http://www.deloreans.co.uk/forum/archive/index.php?thread-5860-11.html

it should point towards the front, aka the pipe of agony.

I think the arrow indicates air flow. So the pipe of agony has the engine vacuum so the arrow should point to that.

[dn010]

I think the arrow indicates air flow. So the pipe of agony has the engine vacuum so the arrow should point to that.

I agree. This is how it is on the B280F, arrow shows the direction of air flow.

[JohnZ]

So are you telling me that I have been rocking my new idle motor backwards all these months? :(

Anyway I should be checking for the culprit for the idle hunting elsewhere then! I'll run some tests one day... :)

Also, I'll check with Arran from DeLoreanGo, maybe their unit must be installed the opposite way...? Which is what this thread by Dave was all about in the first place!

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[glockworks21]

start the car cold next time and while it idle hunting unplug the ism and see what happens.. If it smooths out let me/us know...

I cleaned and oiled the original ism once and it did nothing... I replaced it with the smaller dgo one.. That failed fairly quickly(couple months maybe) I decided to put the original back in and see what happens and it worked perfectly.. point being maybe the original needed to sit awhile and soak in the oil and what not before it freed up... IDK my two cents...

I have a very easy pipe of agony hack... I will try and get pic.....


Dave

[JohnZ]

Alright so I will try to do this test and get back!

also, I will try to clean the old motor, which was fine and I replaced some months ago because I had this terrible noise and I suspected it was the ISM when it wasn't, I will try to put it back on the car to see if this old part is well and better integrated with the system! Honestly at first it seemed that the noise was gone, but after a few days it came back full force! More on that on the specific thread :)

And to be honest the idling worsened a bit after I put on the smaller unit... I was happy because the noise was gone so I never really put the old one again... I hope I did not scrapped it

Any suggestions on how to properly clean the mechanism? I'll browse the forum for some additional infos!

Thanks guys! :)

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[iflights]

Alert-Now the DGO web page for the ISM says the arrow should be facing the brass pipe (the pipe of agony).

[JohnZ]

Yes, I had a chat with Arran and he sorted it out and changed the description on the website! Much clearer...

Now everybody can check the correct orientation of their lovely ISM and change it accordingly! :) (mostly to no avail :D )

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[iflights]

Thank you for leading the charge to get the document updated. Mine is installed backwards, but the car idles perfectly at all temps...I hesitate to even touch it now.

[Bitsyncmaster]

I've been thinking about this reversed idle motor. I do think that owner that it fixed his problems must have had a sticky idle motor. I made a small change to my idle ECU software test routine. After it does the slow moving open and close routine for 4 cycles, I then "slam" the idle motor open and closed repeating at 50 ms. intervals until you power off the ECU. I'm thinking I should also do that one time on power up.

The idle motor has very little torque at the extreme closed location. This "slam" should wipe any build up of carbon on the idle motor valve.

[iflights]

OK, I went ahead and reversed the DGO ISM with arrow now pointing towards the aux air pipe. It ran, with a high idle RPM of 1100, once in gear, RPM was dead on at 850.

I have Dave's idle ECU set at 850.

I decided to swap it out and put back in the original Bosch oriented properly. Same results at idle and under power.

Dwell is still swinging 15-25 as expected.

My conclusion, is that it seemed to idle better the original way I had it set up for whatever strange reason.

[JohnZ]

So basically the orientation of the ISM is tailored on each car! So DeLorean's.... :)

Unfortunately I can't find my old motor, I think I trashed it because at the time I thought it was faulty. I had a terrible noise for a long while coming from that area (more on that here https://dmctalk.org/showthread.php?19929-Frightening-squealing-sound-from-the-engine ), so I replaced it and the noise went away... too bad it was just coincidence, and the noise came back after a few months (loose bolts on the intake manifold)... but the ISM was scrapped. I'll be damned!

Luckily the new DGO motor works, but I have to track down the cause of the idle hunting elsewhere...

This thread was a good ride anyways! :)

[David T]

So basically the orientation of the ISM is tailored on each car! So DeLorean's.... :)

Unfortunately I can't find my old motor, I think I trashed it because at the time I thought it was faulty. I had a terrible noise for a long while coming from that area (more on that here https://dmctalk.org/showthread.php?19929-Frightening-squealing-sound-from-the-engine ), so I replaced it and the noise went away... too bad it was just coincidence, and the noise came back after a few months (loose bolts on the intake manifold)... but the ISM was scrapped. I'll be damned!

Luckily the new DGO motor works, but I have to track down the cause of the idle hunting elsewhere...

This thread was a good ride anyways! :)

On one car I fixed that had a bad hunt it turned out to be the distributor. The gaps to the reluctor were all different. Someone must have replaced the impulse coil and messed up the gaps. The usual cause is a vacuum leak affecting the cylinder closest to the leak. Start by checking the compression of all of the cylinders and maybe adjusting the valves. The goal is to get all of the cylinders to fire evenly. That also means gapping the spark plugs as evenly as you can and getting the injectors to open and spray evenly.

[JohnZ]

Thanks David for your precious input.

I have an update: tonight I took the car out, but before that I ran a little test, as suggested by glockworks. While at idle (cold start, and my car usually does this: surge, stable, surge, stable, surge, stable... and when hot it's just surge, surge, surge) I unplugged the ISM. The result: the idle smoothed out at 800 RPMS! For several minutes! I had never heard that beautiful sound for that long!

Keep in mind that the idle was hunting with the original ISM, then I replaced it about a year ago and nothing ever changed... so there was never really a time in which the new ISM made the idle smooth out.

What do I do with this results? No ISM make the idle smoother... and while it lasted it was a blast! :D

[glockworks21]

https://dmctalk.org/showthread.php?19940-ISM-guidance&highlight=glockworks21

[glockworks21]

now at this point i had done vod, plugs, wires, injectors all new vacuum lines and probably 10 other things i forgot about. going back to the oe ism that was sitting in a plastic bin for months after i cleaned and oiled it solved my problem.
If it smooths out when unplugged you would think it was the problem... IDK.


as i read back that ism lasted about a year.. not a couple months... where does the time go

[Bitsyncmaster]

Here is why vacuum leaks may cause hunting. With a vacuum leak your idle motor has to run more closed. When it's running more closed it has less torque to move it's valve. Well the same would go for having the curb idle screw to far in (it's a vacuum leak). So if your problem is the idle motor, backing that curb idle screw out more will make the idle motor run more open. But you may get to a point of when you take your foot off the gas the idle RPM undershoots.

[glockworks21]

smoke test?

[JohnZ]

So do I replace the ISM with an old unit? Or do I mess with the curb Idle screw until I find the perfect balance?

The new ISM I put about one year ago never gave me a stable idle, not even the first time I fired the car up after the replacement... I refuse to think that it was already faulty!

I will definitely try to do a smoke test!

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[JohnZ]

One thing I was reflecting about: first and foremost it is imperative that if something is off it must be addressed. I think it's always mandatory to have things work as intended, and idle speed makes no exceptions: I should absolutely tackle this unpleasant problem that I had since the day I got the car (2013), because things must work as designed, to the maximum extent possible.

BUT the question is: aside from the ugliness of the sound, does the idle surging technically represent a real practical problem? Have I been damaging things all these years? How does this reflect on the actual driving?

I just wish to know how this feature impacts on regular driving and usage of the car! Maybe not much, but, as I said, I'm determined to address this once and for all!

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[Bitsyncmaster]

BUT the question is: aside from the ugliness of the sound, does the idle surging technically represent a real practical problem? Have I been damaging things all these years? How does this reflect on the actual driving?
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I guess it depends on how bad and how often the idle hunt is. Also it may have more impact on a car with an automatic transmission since you don't take it out of gear at a stop (still a little forward force).

[JohnZ]

Ok! In the meantime I did another test I found on the forum: I unplugged the idle ECU and the value went up to over 2000s RPM! This means the ECU works, right? I plugged it in and the idle went down (surging as usual).

I will try and get my dad to help me to see if the ISM works by looking into the pipe while he put the key in the second position....

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[David T]

The reason you have a "hunting" idle with the idle motor is when the idle system detects that the idle is low because a cylinder is not firing right, it signals the idle motor to increase the idle. By the time it has increased the idle you are on another cylinder that is working well and now the idle is too high. There is inherent lag in the system and that is why you must try to make all of the cylinders function as equally as you can. A cylinder can be affected by fuel, valve adjustment, spark, and vacuum leaks. All adjustments must be as equal as you can make them to have a smooth idle. The idle system is not the problem, it is the symptom. A smoke test is one way to find if you have a vacuum leak. A vacuum leak will lean out the cylinder closest to the leak and make it fire less efficiently slowing down the motor. A bad fuel injector can also do that, as can low compression. When I was testing a lot of cars the most common leak was the rubber seal on the fuel injectors. They get hard from the heat and don't seal well.

[JohnZ]

What you say it's true, and while I don't think my engine is neither damaged nor overabused in its internals, what sits outside can crack, get crusty, be inefficient over time! It's now paramount, after 12 years, that I perform a smoke test to see what's going on! I also read some of your old posts about that, and I think I will seal the air metering unit plate and stick the smoker's pipe into the hose to the oil filler... that should work, isnt' it? I'm really curious about the results, and from then on I will be able to track leaks and stuff!

I play in a band, I remember a while ago we had a smoke machine for show purposes... I gotta find it and use it!

Thanks for the support... I will solve this thing sooner or later!

[Bitsyncmaster]

The reason you have a "hunting" idle with the idle motor is when the idle system detects that the idle is low because a cylinder is not firing right, it signals the idle motor to increase the idle. By the time it has increased the idle you are on another cylinder that is working well and now the idle is too high. There is inherent lag in the system and that is why you must try to make all of the cylinders function as equally as you can. A cylinder can be affected by fuel, valve adjustment, spark, and vacuum leaks. All adjustments must be as equal as you can make them to have a smooth idle. The idle system is not the problem, it is the symptom. A smoke test is one way to find if you have a vacuum leak. A vacuum leak will lean out the cylinder closest to the leak and make it fire less efficiently slowing down the motor. A bad fuel injector can also do that, as can low compression. When I was testing a lot of cars the most common leak was the rubber seal on the fuel injectors. They get hard from the heat and don't seal well.

The idle ECU takes many ignition pulses to get an RPM reading. So yes the delay is one problem but it does not sense RPM variations of one cylinder.

[Rich]

Where to inject the smoke to the car's air intake system?

I prefer to inject the smoke at the large vacuum nipple at the upper right rear of the intake manifold, the source of engine vacuum to the rest of the car. It's easily accessed and it's close to most of the potential leak points.

Pop the rubber hose off of it, then adapt your smoke hose to the nipple.

And seal the air meter intake with the air filter box removed. A rubber glove is a good option.


It's now paramount, after 12 years, that I perform a smoke test to see what's going on! I also read some of your old posts about that, and I think I will seal the air metering unit plate and stick the smoker's pipe into the hose to the oil filler... that should work, isnt' it?

[dn010]

Also a good idea to pop the charcoal canister out and check those lines, otherwise it's hidden in the pontoon and you can't really see what is going on with it. Also a good idea to have a vacuum line routing diagram handy to double check you have everything going to where it is supposed to go.

[Bitsyncmaster]

I've been thinking about this reversed idle motor. I do think that owner that it fixed his problems must have had a sticky idle motor. I made a small change to my idle ECU software test routine. After it does the slow moving open and close routine for 4 cycles, I then "slam" the idle motor open and closed repeating at 50 ms. intervals until you power off the ECU. I'm thinking I should also do that one time on power up.

The idle motor has very little torque at the extreme closed location. This "slam" should wipe any build up of carbon on the idle motor valve.

I implemented the one time "slam" at power up. This is the first software change in 15 years. All new units will have this change. If you want it programed into your older unit, I can do that no charge if you pay return postage. Or if we meet at a tech session I can do it there.

The more I think about it the more I think this will help if your idle motor is getting dirty.

[JohnZ]

...OR you can come to Eurofest 2026 with a bunch of improved Lambda and Idle ECUs and do some business! :D

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[JohnZ]

As for the vacuum lines and testing...thank you both for the advice! I think I know the pipe to you're talking about, Rich! I'll keep you posted! (Will be a long wait I'm afraid)

As for the charcoal canister...I think it's one of those things I never checked, not even opened up the plate to check how it looks...will try! Is it something that is supposed to be cleaned from time to time? I will look into it!

Thank you all guys :)

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[David T]

On the subject of the vacuum canister, there is a filter on the bottom of it that can be cleaned or replaced and the hose coming out of the bottom can get plugged up with insect debris. There is a rubber cap on top that is deteriorated on EVERY car, just replace it. I inject the smoke into the small hose that attaches to the air filter box. Remove the air filter box and seal the intake over the sensor plate. I don't know if a smoke machine from a DJ has enough pressure. You need a small amount of pressure in addition to the smoke. It takes a moment to build enough pressure to see smoke leaking out. On one car I had so many leaks it was hard to figure them all out, smoke came out everywhere! We tackled them one-by-one. For a quick fix you can wrap teflon tape over the leaky injector seals. On one car it had way too long a bolt holding the air box on, it actually went through and bent a metal plug at the end of the intake manifold and caused a big leak. Once in a while I find a car with no plug over the mixture screw. The air pipe for the idle motor coming out of the mixture unit is another place to inspect. On another car the "O" ring was missing on the cold start valve. Smoke is the only way you are going to find all of these "sneaky" leaks. If you have to, find a shop that has a smoke machine, they should not charge a lot of money to do the test.

[glockworks21]

I bought a autoline smoke machine on amazon for like $70.. I just searched and there are a lot of options in the 50 to 80 range.. good investment that you will end up using more than once...

[JohnZ]

Yesterday I noticed something weird, and I want to know what you guys think.

After a short trip that was parking the car in my garage, the car was warm and the idle was hunting as usual (700~1400 rpm), then the fans kicked in and I let the engine cool down before shutting the car off, as I always do.

While fans were operative the idle stabilized at around 800, it was like magic! It wouldn't surge or mess around, just rock solid 800 rpm... Until the fans turned off, and the hunting started once again.....

Does it make sense to you?

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[Bitsyncmaster]

Yesterday I noticed something weird, and I want to know what you guys think.

After a short trip that was parking the car in my garage, the car was warm and the idle was hunting as usual (700~1400 rpm), then the fans kicked in and I let the engine cool down before shutting the car off, as I always do.

While fans were operative the idle stabilized at around 800, it was like magic! It wouldn't surge or mess around, just rock solid 800 rpm... Until the fans turned off, and the hunting started once again.....

Does it make sense to you?

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With the fans running, you have more load on the engine. Therefor the idle motor has to run a little more open then where it runs with the fans off. Try backing off your curb idle screw a little.

[JohnZ]

Thanks Dave! Are you referring to the idle mixture screw between the FD and the metering plate? the one that has to be plugged, operable with the allen key?

If so, what do you mean by "backing off"? do I turn it clockwise or anticlockwise?

EDIT: I guess maybe you refer to the top brass screw near the manifold tubes? the one with the flathead screwdriver insert?

[Bitsyncmaster]

Thanks Dave! Are you referring to the idle mixture screw between the FD and the metering plate? the one that has to be plugged, operable with the allen key?

If so, what do you mean by "backing off"? do I turn it clockwise or anticlockwise?

EDIT: I guess maybe you refer to the top brass screw near the manifold tubes? the one with the flathead screwdriver insert?

The curb idle screw is the lower screw (below the idle switch screw) on the throttle arm. That is used to prevent your throttle plates from closing all the way closed.

Turn it counter clockwise about a 1/4 turn.