New solution for unstable idle AXR

Hi.
I took my car to the dealership at the beginning of the week to have them check the uneven idle (slight jerking or shaking) as part of my used car warranty. It was noted that the engine control unit ...MQ had already been installed, and that all the common rail injectors had also been replaced with newer ones.
At this point, they didn't know what to do next. Since I'm still in contact with my dealer at the moment (because it's a driving school car and not accident-free), we decided to leave it at that for now.

Today, I got into the car with my laptop and VAG-COM, and I adjusted the idle speed slightly by adapting channel 2. The registered value of 32768 was reduced by me to 32730; as a result, the speed decreased from 904 RPM to approximately 840 RPM.

While driving to work and encountering several traffic lights, I could no longer detect ANY idling roughness . The engine runs very smoothly even at a low idle speed.
I also assume that this will not significantly reduce the oil pressure at idle.

Since there are a few more people in this forum who are 'in the same boat,' this is likely to help some of them.

Hati wrote:

As a result, the speed decreased from 904 RPM to approximately 840 RPM. While driving to work and encountering several traffic lights, I could no longer detect ANY idling roughness . The engine runs very smoothly even at a low idle speed. I also assume that this will not significantly reduce the oil pressure at idle.

Well, "significant" is subjective, but the pressure will definitely decrease.

Hopefully, the LiMa (alternator) output at the reduced idle speed will still be sufficient to power the winter Christmas tree along with all the active electrical gadgets, while also charging the battery .

I would at least temporarily connect a high-resolution analog voltmeter to the cigarette lighter socket and observe it during stop-and-go driving...
... if the needle drops even slightly when the engine is idling, you might one day find yourself unexpectedly unable to start the car in freezing temperatures because the battery charge is no longer sufficient.

Thank you for the tip.
I'll probably test it out tomorrow morning; especially since I'll be driving in the dark then, and I can finally fire up the 'Christmas tree' (presumably referring to some kind of lighting or decoration). Although it makes 60 revolutions per minute, it only completes one revolution per second.

You can also use Vagcom to read the load percentage of your generator. I have also lowered the factory-set idle speed (970 U/min) to 790 U/min, and the regulator only needs to work about 2% more with all consumers turned on (increasing from 30% to 32% overall). The voltage remains the same. However, I also have a larger battery charger with 140A (for a 95Ah battery).
Now, the engine doesn't need 0.5L/h anymore, but 0.3L/h.

As long as you stay within the specified RPM range, there is nothing to worry about.

P.S.: Adjust the idle speed with the engine at operating temperature and with as many consumers as possible turned OFF!

Regarding the charging capacity of the alternator:
It should actually be visible using VCDS, right? At least, I can read the alternator load on mine. If the brightness is already too high with the standard decorative lighting and rear window, I would agree with Ulf and increase the LL (low light) speed again.

Sure, here is the translation of the text from German to English:

"Dirk"

@ulf

'Don't worry about it. On our Passat, the idle speed was 800 revolutions per minute when the engine was warm. That's too low (bad for starting), so I adjusted it (now it's 880 revolutions per minute when warm).' Unfortunately, I couldn't do more, as that's the resonant frequency of the vehicle, which causes the entire vehicle to vibrate.

Best regards, WarLord.

P.S.: Adjust the idle speed with the engine at operating temperature, with as many consumers as possible turned OFF!

I don't understand that now .
When I specify a digital speed setting, it is maintained both in the warm and cold states of the engine (except for an increased idle speed at very cold temperatures shortly after the engine starts).

Hi,

I had also considered lowering the idle speed, but I wonder if that would cause problems when starting.

@Julian: Can you still start or maneuver at 790 RPM in neutral?

Best regards,

Jan.

I don't understand that now .


Simply put, the motor is under load, and the more consumers are turned on (e.g., the alternator has a higher resistance), the greater the load. The low-level setting (LL) should ideally be adjusted to a value that is as low as possible without any load, while the system is in its operating state (warm). Otherwise, the low-level setting configured with consumers might unexpectedly be too high if no consumers are actually connected.

Simply put, the motor is under load, and the more consumers are turned on (e.g., the alternator has a higher resistance), the greater the load. The low-level setting should ideally be adjusted without any load while the system is in operating mode (warm), otherwise, the low-level setting configured with consumers might suddenly be too high if no consumers are present.

That was the case with my old AAZ engine, but it should be properly calibrated on a TDI engine.

@Julian: Can you still start or maneuver at 790 RPM in neutral?


Better than before. I need to drive into a rather narrow underground parking garage, and I usually do that in first gear.
Now I don't have to use the clutch when navigating tight corners, because the car now drives slowly enough in first gear.

The idle speed control is the undisputed champion, it's now very difficult to affect, and the car is extremely maneuverable. I've even been able to develop a better feel for the accelerator pedal. You just need to get used to the lower idle noise at first; that's really all there is to it.

The torque cutoff is also 'longer' in duration, in terms of engine speed.

Hati wrote:

Hi. I took my car to the dealership at the beginning of the week to have them check the uneven idle (slight jerking or shaking) as part of my used car warranty. ... Today, I got into the car with my laptop and VAG-COM, and I adjusted the idle speed slightly by adapting channel 2. The registered value of 32768 was reduced by me to 32730; as a result, the speed decreased from 904 rpm to approximately 840 rpm.

After some time with the ASZ Polo, also running at approximately 840 rpm, I haven't been able to report anything definitively negative so far.
The engine sounds subjectively richer and more confident when idling.

If the 90A lithium battery management system is overloaded, the electronic load management temporarily increases the LL (low-speed) motor speed to approximately 1000 rpm, for example, after cold starts with afterglow.

With my ALH Ibiza, I wanted to do the same thing because the diesel engine sounded a bit rougher compared to the Polo.
Unfortunately, when trying to lower the speed, it stops at 32743, which is just one VAGCOM grid (21 rpm) and is roughly confirmed by the tachometer.
By the way, the same thing happened at the AFN golf tournament.

It appears that the adaptation is possible in steps of 1 rpm.
A reduction of 68 in the ASZ results in approximately 70 rpm less, while a reduction of 25 in the ALH results in approximately 21 rpm less.

Hi,

*dusting*

Quote:

It appears that the adaptation is possible in steps of 1 rpm. A reduction of 68 in the ASZ results in approximately 70 rpm less, while a reduction of 25 in the ALH results in approximately 21 rpm less.

ALH and ASV are quite similar, but in my attempts (now that the power issue is resolved), I was just getting slightly different results.

"The starting value was 32768. I experimented with values between 32700 and 32800, which should theoretically produce a change of about 100 RPM, according to Ulf's theory." But it didn't really happen.

Normally, VAGCOM displayed a value of 903, with occasional jumps to 924, suggesting that the engine speed was likely at the sampling limit. With a value of 32800, we observed 945 readings, with occasional outliers reaching 924 (so this value might be appropriate). Conversely, when the value was 32700, we expected 882 RPM, but occasionally saw spikes up to 903.

However, I must mention that the machine was cold during the tests (oil temperature 30...40 degrees Celsius), but the afterglow function was already turned off, and all consumers were switched off (although I always see a "0" in the "Load" field, regardless of what I turn on).

So, the question is whether the engine temperature somehow plays a role in the adaptation process and prevents certain reductions. Has anyone else observed something similar?

Finally, I chose 32790 for the first setting (which is roughly just under 940), because it allowed me to avoid the resonant frequencies of various parts of the suspension arm, and because it's likely better for the battery in short-distance city driving in the winter (at least potentially... Julian's observations from earlier suggest otherwise). Let's see... when it's a bit warmer, I'll definitely adjust it downwards when the engine is warm.

Best regards,

Jan.