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Rough/Bad idle (1973 VW412 1,7L Fuel Injection Engine)
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Jun246
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PostPosted: Fri Apr 30, 2021 2:55 am    Post subject: Rough/Bad idle (1973 VW412 1,7L Fuel Injection Engine) Reply with quote

Hello

If you could give me your advice for solving the problem, it would be highly appreciated.

I recently bought VW412 (1973 Model) with 1.7L fuel Injection Engine.
Mileage is 85,000km (ca. 53000 miles) and this car is mounted 3 speed AT.

From the beginning, it is observed that the Engine idle at cold/stating is unstable. This problem is occurred until the Engine gets hot (May be until after 30 minutes run).
No Engine stall happened so far but sometimes it was almost stalled.

Even while the problem is observed, when you accelerate to drive the problem is gone. But if the Engine speed gets low again (Sometime even when still driving) , the problem happen again.

How long the problem continue is depends. In the better case, after 15mins run the problem is gone. In the worst case, even after 60mins the problem is still exiting.


I have no idea if the problem is caused by "Airflow" or "Ignition" or "Fuel".
On the other hand I think this is known problem by many of VW Type4 Engine users.

Can you please give me how to fix the problem? If I could I want to try to do it by myself. (If not I will find and ask VW shop for the remedy work)

Your advice is highly appreciated.


JUN

P.S. I am Japanese, Sorry for my poor English.


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Pepperbilly
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PostPosted: Fri Apr 30, 2021 8:23 pm    Post subject: Re: Rough/Bad idle (1973 VW412 1,7L Fuel Injection Engine) Reply with quote

Hi JUN,

Welcome to the 412 world. You have a really nice looking car with very few miles!
I tell people when they have running problems to check all basic engine settings first. That means your valves need to be set correctly. Ignition timing is also very important. Is your fuel filter clean? Install a new one if you do not know. Check all your fuel lines... a car this old needs good lines otherwise you risk having a fire. Check all these things first and then we can go from there.

Bill
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Jun246
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PostPosted: Sat May 01, 2021 1:40 am    Post subject: Re: Rough/Bad idle (1973 VW412 1,7L Fuel Injection Engine) Reply with quote

Hello Bill

Thank you for your kind advice !!
I will check all basic setting as you suggested.
Although it will take certain time I will do it and come back !!

Again many thanks,


JUN Laughing


P.S. I forgot one thing to tell. When the shift position is at "N" Engine run at idle is stable and no problem. When it is at "D" with pressing break pedal, Engine speed drop down and the problem happen.
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PostPosted: Sat May 01, 2021 9:49 am    Post subject: Re: Rough/Bad idle (1973 VW412 1,7L Fuel Injection Engine) Reply with quote

JUN,

Ok, that was very important to know! It sounds like the idle stabilizer is not set correctly. This part helps to make a stable and consistent idle when in any gear.. There is a procedure to set it. It is not always easy to set. I have included a photo... it is the gold colored part.

Bill
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raygreenwood
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PostPosted: Sat May 01, 2021 11:36 am    Post subject: Re: Rough/Bad idle (1973 VW412 1,7L Fuel Injection Engine) Reply with quote

I will try to get a reply in today. Yes....it could be the idle stabilizer.....but there can be a range of load/vacuum based issues.

More to come. Ray
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PostPosted: Sat May 01, 2021 5:32 pm    Post subject: Re: Rough/Bad idle (1973 VW412 1,7L Fuel Injection Engine) Reply with quote

Hello Bill and Ray,

Thank you for your attention and advice!!
Here is my test drive result. I do the same tomorrow.

Outside temp.: 13deg C (55deg F)
Weather : Sunny
Road : Paved
Test course :
-Start-60mins : City
-60-100mins : Mountain area
-100-180mins: City

Findings.
1. Within 3mins from driving start, the subjected problem was observed when the car is stopped with the shift lever is at EITHER "D" or "N". Engine idle speed didn't go up when I shifted from "D" to "N". (I could not see differences between the both gear position)

2. After 3mins up to 60mins, the problem was observed when the car is stopped with the shift lever is at "D". When I moved the lever from "D" to "N", Engine idle speed went up and run without the problem.

3. After 60mins up to 120mins, the situation was basically the same as 2. But the level of the problem got better. I can describe the problem like a "slight breathing or Pulsating"

4. After 120mins up to 180miins, the situation was basically the same as 2. But the level of the problem got worse sometimes than the above 3


Summary
-The problem was confirmed when the Engine was also hot.
-The problem was confirmed when the car is stopped with Engine idling at "D".
-Basically Engine idle at "N" is fine. However, the problem was also confirmed when the Engine idling at "N" . This is applicable only within 3mins after the Engine run.
.During the test drive, it was not found any other Engine/Power train related issues, except the subjected problem.

I will do the same tomorrow.

Again many thanks for your excellent advice!! Smile

JUN
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Jun246
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PostPosted: Sat May 01, 2021 6:08 pm    Post subject: Re: Rough/Bad idle (1973 VW412 1,7L Fuel Injection Engine) Reply with quote

Hello

Further to my previous posting, the problem was also confirmed when driving at low Engine speed (Car speed less than 40kph, 25mph). Car can move but it is not smooth until car speed get above 40kph.

I guess the subjected problem can be happened regardless driving or idling. when the problem happens if you accelerate and car speed get above 40kph, now you cannot feel any abnormality on driving.


JUN
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raygreenwood
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PostPosted: Sun May 02, 2021 8:39 am    Post subject: Re: Rough/Bad idle (1973 VW412 1,7L Fuel Injection Engine) Reply with quote

By the way.....your English is just fine!

Better than mine some days! Very Happy

This post will be long.....and will not answer your question today.....but i will get there! Wink

Ok.......the question and issue at hand.....is driving and idling problems....with D-jet injection and the automatic transmission.

The answer to your problem will be long and drawn out. This is why I have been waiting to answer your question.

It could be one simple thing/item/problem that needs adjusting or correcting.....but it is rarely that simple. Maybe half of the time at best.

It is usually a stack up of several issues........and because of the type of fuel injection we have......characterized by its sensitivity to EVERY INPUT.....causing changes to OUTPUT......those changes to power output and stability of power output......heavily affect the automatic transmission more than the manual tranmission.

And.....changes that affect the automatic transmission......affect the level of load transmitted back to the engine......which affects the load sensing of the EFI system.....which affects the power output of the engine.....which affects the automatic transmission.....which affects the loading of the engine......etc....etc....etc.....etc..... Rolling Eyes

Only in the Haynes manual in one or two cryptic lines and in the brown Bentley type 3 car manual.....again....maybe one cryptic line in the text......is this symbiotic positive/negative relationship.....referred to.

To be fair.....the manual transmission cars have the same power output to transmission load issues......but the manual transmission cars have a different torque band and shift point, the transmission has no vacuum control and the deceleration valve works differently and there is no throttle positioner.......so......the manual transmission cars with D-jet are missing some of the "sensitivity" of the automatic cars with D-jet.

So.....between the type 3 forum and the 411/412 forum.....there are many, many threads where we solve this EXACT problem.....or versions of it.

There is also the type 3 "Fuel injection relief here" sticky/thread.....247 pages long at the moment Rolling Eyes . Wink .....with tons of excellent information regarding D-jet injection....mostly type 3 but some type 4.....and the "Automatic +D-jet" issues have been solved numerous times within that sticky.

There is also the "D-jet Phd: Newbies need not enter, advanced EFI tuning" sticky.....currently 19 long pages.....of excellent information...wherein the "Automatic+ D-jet " issues have also been addressed.

The problem with all of this archived data:

Many times we have started threads to address "Automatic + D-jet" driveability issues......and a HUGE proportion of the time and effort is spent getting the person asking the question to UNDERSTAND.....exactly how the D-jet system works, what it is sensitive to, why its different now compared to when it was new and what must be set straight/correct/new/repaired.....before you can accurately diagnose or correct some problems.

In a lot of these "Automatic + D-jet" threads .....the car owner asking the question.....either does not want to do all of the corrections needed....or does not have the time, instruments or money to do the work or corrections......and sometimes is not interested in getting the problem "fixed".....but js mainly just interested in getting it "good enough". This strings the thread out.....sometimes for a year or more.....and does not really produce a DEFINITIVE answer......and its VERY hard to search for with the serach function.....if you do not know the terminology or even what the problem you have is called/named.

You get lots of good and TRUE tuning information.....but you also get lots of filler stories and cross conversation that.....while its interesting and fun!......makes it to where anyone who does not know the hardcore basics of D-jet.....has to sift through HUNDREDS of pages across three forums.....type 3, 411 and 412 and Porsche 914......just to get enough grasp of the system to solve the issue......unless they get lucky.

This causes car owners who are just trying to solve an annoying problem......to approach the problem piecemeal. They may fix it but never know why. Or they give up.....happens a lot.

And because these issues have been asked so many times.....there is a small habit of just telling new owners who ask these same questions......to go read the hundreds of pages of stuff and use the search function......and then come back if that has not answered the question. That......does not help.

And.....while the type 3 cars with D-jet + Automatic......are almost the same.....they are not the same.


What I am proposing is to start a SPECIFIC thread "Automatic transmission +D-jet" driveability tuning.

The first page or so......will be just explaining the sensitivies and operation of the D-Jet EFI system.....for 411 and 412 only. I do not want to get hung up in all of the years/era variations that type 3 cars had.....essentially three different main versions of D-jet. I also do not want to make a huge NEW "this is how D-jet works"....page.

I am speaking of system sensitivities. What changes to what parts cause changes to fueling and therefore power output. Like:
Sensors 1 and 2
MPS.......which is the key to 100% of this
Grounds and power
Fuel pressure and stability
Vacuum, vacuum, vacuum
Ignition....spark, advance, stability
Wiring, wiring, wiring.....connectivity

Critical secondary sub-component adjustments....TVS, AAR, throttle positioner, deceleration valve......which leverage many of the components above.

This will be a simple list of what each of these parts/components do, what affects them, how they affect each other....and most importantly what each does to power output.

Then the Automatic transmission itself.....its vacuum control system, its pressure control system, its torque converter ....and the relationship it has with the power supplied to it and the load it supplies to the engine.

I do NOT want to make a new sticky thread that ends up hundreds of pages long where everyone adds in their story and problem.

I want to keep it as a clear starting place.....relatively short read.....so people can first get a grasp of what they need to correct and measure on their car and engine.....BEFORE.....starting their own thread on their car with "Automatic +D-jet" issues. Yes....anyone can add in information as they find something useful.....that is true across the board.

I will get into the details of trying to help Jun246 with his issues..... Very Happy .....but I think in the long run we can do better to help make it not such a long drawn out, painful LEARNING PROCESS.....when it should be just a diagnosis process.

Ray
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Pepperbilly
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PostPosted: Sun May 02, 2021 9:13 am    Post subject: Re: Rough/Bad idle (1973 VW412 1,7L Fuel Injection Engine) Reply with quote

JUN,

You mentioned during your test drive that you experienced a “pulsating” or a “breathing” type of idle. This is very representative of a misadjusted or misbehaving idle stabilizer as I described. Ray is correct that it could be many things causing this... vacuum leaks being one of the biggest. Hopefully all your basic engine and ignition settings are spot on. This system relies very heavily on ALL vacuum lines and connections having no leaks... do not overlook this. If you need the procedure for setting the idle stabilizer I can get that to you.

Bill
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PostPosted: Sun May 02, 2021 12:17 pm    Post subject: Re: Rough/Bad idle (1973 VW412 1,7L Fuel Injection Engine) Reply with quote

Pepperbilly wrote:
JUN,

You mentioned during your test drive that you experienced a “pulsating” or a “breathing” type of idle. This is very representative of a misadjusted or misbehaving idle stabilizer as I described. Ray is correct that it could be many things causing this... vacuum leaks being one of the biggest. Hopefully all your basic engine and ignition settings are spot on. This system relies very heavily on ALL vacuum lines and connections having no leaks... do not overlook this. If you need the procedure for setting the idle stabilizer I can get that to you.

Bill


Yes.....it could be the idle stabilizer adjustment as has been mentioned....but bear in mind.....the idle stabilizer unit itself....can have their own issues over time (age related).

What Pepperbilly is getting at though....is that its connected to the manifold vacuum system.

The idle stabilizer "MAY" be perfectly fine and actually adjusted perfectly...but may be being affected by any number of vacuum leaks or wear items.......and most commonly....overall wear to the engine that may have reduced or altered vacuum signature that operates the idler stabilizer.....OR.....fuel mixture variations that cause fluctuations in vacuum.....OR.....wiring issues that cause variations in fuel mixture that cause variations in vacuum signature.....OR....ignition issues that cause variation to fuel mixture and advance that cause variations in vacuum signature......OR.....and this is a big one....variations in shift point, pressure adjustment and decoupling of torque converter in the transmission....that causes load variations...that affect fuel mixture....that affect vacuum signature....that affect the idle stabilizer.

See....the idle stabilizer in these engines....is the "tail end of the dog" ! It is DOWNSTREAM....a FINAL tweak.....and not upstream. Very Happy

If you can first verify that the idle stabilizer itself is not leaking or defective....and then take one single shot at normal adjustment......just a tweak...and if that does not fix it....LEAVE IT ALONE......and instead, methodically fix all of the other items that affect fuel and vacuum.

Then you can most probably.....properly adjust the idle stabilizer.

Here is a start....to just the idle stabilizer...or "throttle kicker" part.

https://www.thesamba.com/vw/forum/viewtopic.php?p=8164179&highlight=#8164179

By the way...I hate using the term "idle stabilizer"...with this part. That is NOT its function....but the name is fine for now Very Happy

This next comment is VERY IMPORTANT....and illustrates why I am making a big deal out of this.

This unit that we are calling the "idle stabilizer"....should ONLY be operating for about 2 seconds....as the car comes to a stop.

Why?

Because its EXACT function is to prevent the engine idle from dropping too low (potentially stalling the engine) from when the car is driving/rolling with the torque converter fluid coupled to the engine.....to when the car stops.

Because of the low stall point of the torque converter in these cars....it can take a second or two for the torque converter internal pressure to drop enough to decouple the transmission from the engine to allow idle without loading the engine.

This is the ONLY function of the idle stabilizer/throttle kicker.

It should have "0" function on stabilizing or changing engine idle....at any other time. If that is happening.....you have other malfunctions elsewhere in the system.

THINK about that last sentence....and some of your tests and observations!


If you are having idle fluctuations at any speed and temperature in any gear OTHER than DRIVE, 2 or 1......the idle stabilizer should not be operating at all. The transmission should be decoupled from the engine load in N or P. Wink

Ray
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PostPosted: Sun May 02, 2021 1:12 pm    Post subject: Re: Rough/Bad idle (1973 VW412 1,7L Fuel Injection Engine) Reply with quote

Thanks Ray for the support on this subject...you beat me to it. Hopefully this is JUN's only problem...

Bill
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PostPosted: Sun May 02, 2021 6:26 pm    Post subject: Re: Rough/Bad idle (1973 VW412 1,7L Fuel Injection Engine) Reply with quote

And, by the way, your command of the English language is way better than our command of the Japanese language! So is your 412 Japanese market? Right hand drive? Beautiful car.
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PostPosted: Mon May 03, 2021 2:07 am    Post subject: Re: Rough/Bad idle (1973 VW412 1,7L Fuel Injection Engine) Reply with quote

Hello Ray and Bill,

I do appreciate your super great advice!!
Firstly, I will check the exiting relative information as you mentioned.
By the way I did the test today also, the result was the same as the first one.

Once again, thank you for your kind support !!


JUN Very Happy
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Jun246
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PostPosted: Mon May 03, 2021 2:11 am    Post subject: Re: Rough/Bad idle (1973 VW412 1,7L Fuel Injection Engine) Reply with quote

Hello Chris,

This 412 is official import car for Japanese market. It is Right hand drive.


JUN
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PostPosted: Mon May 03, 2021 8:57 pm    Post subject: Re: Rough/Bad idle (1973 VW412 1,7L Fuel Injection Engine) Reply with quote

Very nice Jun. Is this a restored vehicle, or a (very) well preserved example?

Chris
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PostPosted: Tue May 04, 2021 2:40 am    Post subject: Re: Rough/Bad idle (1973 VW412 1,7L Fuel Injection Engine) Reply with quote

Hello Chris,

It is not restored, is well maintained and storage car. I have almost spent 15 years to find it, It is extremely hard to find Type4 car and also its parts in Japan due to the poor sales result of the model here in the early 70's.


JUN
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PostPosted: Wed May 05, 2021 8:57 pm    Post subject: Re: Rough/Bad idle (1973 VW412 1,7L Fuel Injection Engine) Reply with quote

Indeed Jun, they didn’t gain much favor in any market (except maybe the home market? Not sure). That’s a topic of some discussion here on the Samba and elsewhere. They were much dynamically improved over the type 3 or type 1 (beetle).

Chris
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PostPosted: Thu May 06, 2021 9:20 am    Post subject: Re: Rough/Bad idle (1973 VW412 1,7L Fuel Injection Engine) Reply with quote

AS suggested above, the simplest advice is to do a tune-up on it first: valves, timing, idle...and a thorough check of hoses and seals (including injector seals), loose wiring, and voltage. Usually this reveals something out of adjustment, loose, or leaking. Even if it doesn't, having the adjustments right to spec makes further diagnosis easier. If you are stumped and take it to a specialist (if you can find one!), these steps will make their job easier, and cheaper for you.

The problem with this vintage of engine control is that it is like a chain of links... one weak element, and the open-loop system runs poorly. Worse, you can get a cascade of "slightly wrong" settings and conditions that can combine to make things much worse, or even make entirely new symptoms that are unrelated to the root cause.

This is why cars of the mid '70s and early '80s got such a bad reputation... the use of closed loop systems made huge strides in engine reliability and economy, and of course, emissions.

Chasing "ghosts" and throwing parts at a problem leads to frustration and expense.

This is good advice for any air cooled VW, but especially so for later models with more complex emission control equipment.

That's one of the nicest looking Type 4s I've seen, share more photos please!
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PostPosted: Fri May 14, 2021 6:44 am    Post subject: Re: Rough/Bad idle (1973 VW412 1,7L Fuel Injection Engine) Reply with quote

Hello KTPhil

Thank you for your suggestion !!
I will try to find the "ghosts"... Surprised


JUN


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PostPosted: Fri May 14, 2021 12:45 pm    Post subject: Re: Rough/Bad idle (1973 VW412 1,7L Fuel Injection Engine) Reply with quote

Thats a nice looking car! Can you snap a picture of the chrome finger guard plates on your door handles please? Very Happy

Ray
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