Strange vibrations and jolting in A6 AFB

Hello everyone,

My father's A6, manufactured in November 1999, with 140,000 km, also has an AFB engine like mine, but it's a Quattro with a Tiptronic transmission, and it's exhibiting a very strange phenomenon that I can't quite figure out. Firstly, the mass airflow sensor (MAF) seems to be defective. The logged values only show a maximum value of just under 700.

Secondly, the boost pressure control system exhibits significant overshooting. The pressure spikes up to 2600 mBar and then only drops to 1800 mBar after about 3 seconds, before it slowly increases again. After a short drive, the error memory repeatedly displays a message like 'Boost pressure exceeds regulation limit sporadically' or something similar. According to Audi, the term 'sporadically' actually means it's not really an error... it could be caused by so many things, and it should be disregarded.'Quite a statement from a so-called 'expert company,' wouldn't you say?'

Aber ich denke das diese zwei Probleme wohl nichts mit dem Ruckeln was mich so stutzig mach zu tun hat. Wenn man in der 5. Fahrstufe (Tiptronic) von höheren Geschwindigkeiten kommt und dann bei etwa 1600 U/min wieder aufs Gas tritt, merkt man zeitweise ein starkes Vibrieren oder ein sehr starkes hartes regelmäßiges Ruckeln. Man wird regelrecht im Wagen durchgeschüttelt. Wenn man dann von Hand in die 4. FaIf you reduce the heat level, the problem will immediately disappear.
Does anyone have any idea what this could be? I've never heard of anything like it, and I have no idea what it might be right now.
For this reason, I would be very grateful for some tips!

Regards,

DENNIS

Hello everyone,

ich habe heute mal die Gelegenheit gehabt die Sache ausgiebiger zu testen. Der Fehler mit dem Ruckeln ist in jeder Fahrstufe reproduzierbar. Am einfachsten funktioniert es aber in der 4. und 5. Fahrstufe. Wenn man z.B. in der 3. Fahrstufe den Wagen in Drehzahlbereiche von etwa 3000-3500 U/min hatte und dann plötzlich den Fuß von Gas nimmt, schaltet die Tiptronic in die nächste oder übernächste Fahrstufe. Soweit so gut. Wenn man dann aber wieder bei 1500-2000 U/min plötlich wieder Gas gibt (ohne das die Tiptronic zurückschaltet) fängt der Wagen meist sofort an stark zu ruckeln, so das regelrecht ein mechanisches Geräusch hört. Dabei fängt er auch sehr stark an zu rußen, was man bei Tag sehr deutlich im Rückspiegel sieht. Wenn icThen increase the speed setting again.'When I shift gears and the engine speed goes above approximately 3000 RPM, everything suddenly disappears. Even when I'm starting from a stop, for example at a traffic light, and accelerating continuously, this doesn't happen. It only occurs when I take my foot off the gas pedal and then try to accelerate again after a while; in those cases, it only works about 50% of the time.'
I was just at Audi and test drove one of their 'friendly' cars. Fortunately, it worked out for him too. However, he said he's never had this kind of problem before and doesn't even know where to start looking.
My suspicion is increasingly that it's the ESP.
Does anyone among you perhaps have an idea?

(A6, AFB engine, manufactured in 10/1999, 140,000 km, tiptronic transmission, quattro all-wheel drive)


Regards,

DENNIS

Hi,
Generally, you should always address any known issues first. Or are you planning to sell the car?

Furthermore, Ulf recently wrote something about stuttering and faulty mass airflow sensors.
That should be a good enough reason to exchange it.

However, some time ago there was a thread about a potentially similar problem (I've forgotten the details), but it turned out to be the pump. -> Use the search function.

There is also an entry on this topic by Michael II.

Das Thema ist 'vibrationen bei niedrigen drehzahlen' und wurde (u.a. auch von mir) bereits des öfteren behandelt, im Artikel von Michael II geht es generell um bekannte Probleme mit dem sch..... AFB engine.

Have fun searching; it's likely to bring up a lot of results...

Stefan.

Hello Stefan,

I had already read this post by Michael II before I wrote my own. I had already checked the idle speed control, and it seems to be within the normal range. However, I didn't check it with the gear engaged, because at the time I didn't know that you were supposed to do that. But the values were within the normal range even without the gear engaged.
The workshop has already replaced the mass airflow sensor, which supposedly fixed the soot issue but not the jerking. I don't understand how that's possible, since the soot only appeared when there was also jerking... Otherwise, they are currently focusing on the Tiptronic transmission and want to change its oil.
Luckily, all of these issues are covered by the VAG warranty.


Regards,

DENNIS

Hello!

Finally, someone else has the same problem as me!

I think you might be having the same problem. I've written quite a bit about it here already. (Try searching for it!)

I've now given up and will be taking my car to the Audi factory soon. So far, I haven't been able to find anyone who can help me, and I've already invested several thousand euros.

Regards,

Wolfgang.

P.S.: Where is the car parked?

Hello Wolfgang,

I assume you're referring to your post about the missing cylinders after the BAB trip!?
I think my problem might be something else, or that it's manifesting differently now.

Komme gerade wieder von der Audi-Werkstatt. Nachdem sie ja zu Anfang den defekten LMM getauscht haben, tritt das Problem schon fast bei jedem Beschleunigen auf. Allerdings soll das starke Rußen weg sein... Mann kann ohne ihn erst über die BAB zu jagen schon im lauwarmen Zustand beschleunigen und man wird durchgeschüttelt. Der Meister meinte das es so extrem ist, wie er es noch nie erlebt hat. Momentan sind sie gerade dabei zwei Düsen zu tauschen die wohl außerhald der Tolleranz liegen (Beitrag von Michael II). Gleichzeitig wollen sie auch nochmal den Förderbeginn prüfen, der aber meiner Meinung nach stimmt. Zumindest was ich im Messwerteblock im Leerlauf ablesen konnte. Wenn das nicht hilft, sind sie mit ihrem Latein am Ende. SThey have already received a request.I contacted Audi in Ingolstadt about this, but they have not yet provided a response.
They are still considering two possibilities, but they are reluctant to test them directly. One possibility is that the problem might be related to the drivetrain (e.g., the Tiptronic transmission), or it could potentially be caused by the ESP (Electronic Stability Program).
What's noticeable to me is that the new LMM (likely referring to a mass airflow sensor) is now correctly measuring the air mass again (it was previously only reading 680, but is now around 860). This, if I'm not mistaken, should also lead to a slightly higher fuel injection amount, and consequently, the torque should also increase. Could both possibilities, the transmission (Getribe) and the ESP (Electronic Stability Program), potentially be considered as causes of the problem?

Perhaps Audi should include the following in the fine print of the purchase agreement: 'There is NO guarantee that Audi will be able to repair the vehicle if a fault occurs.' It certainly seems to me that they are selling a product that cannot be repaired by anyone in the event of a problem, and that the costs will be borne by the customer.
Fortunately, the car still has a used car warranty. However, there is a deductible of 10%. This doesn't sound like much, but in the case of a transmission replacement, it would amount to around 800-900 euros, *without* the guarantee that the warranty will fix the problem!

So, let's see what news Monday brings...

@Wolfgang: The car is in Mainz.


Best regards, and wishing everyone a lovely and sunny weekend!

DENNIS

The data below does NOT refer to the vehicle in question!!
The vehicle in question is an Audi A6, manufactured in November 1999, with a Quattro all-wheel drive system, Tiptronic transmission, and 140,000 kilometers (approximately 87,000 miles) on the odometer.

The symptom has also changed for me.

I can only drive exactly 155 km/h on the highway, and no faster. If I try to drive at a 'faster pace' on a country road, the same thing happens.

It feels like three cylinders of the engine bank are missing. The entire powertrain vibrates. However, if I keep driving for a while, it disappears again.

Have you checked to see if both valve covers are sealed properly? I've actually developed a different theory. (I can't seem to get the valve cover on the right bank to seal, even with a new valve cover gasket.)

At high engine speeds, the oil may not be able to drain quickly enough from the cylinder head. This creates a buildup of oil in the head, which can cause the hydraulic lifters to malfunction. The V6 TDI engine has two valves in the 'V' that regulate the oil return from the cylinder heads. I suspect that these valves may not be functioning correctly.

Unfortunately, the valves are not easy to replace. (I should have helped with the pump replacement.)

Otherwise, I'm at a loss.

By the way, if I stay in these vibrations for long enough, I can also find them reflected in the air mass signal.

Please keep me updated.

Regards,

Wolfgang.

P.S.: If you could send me your phone number via private message, I might be able to stop by sometime. I'm often in Frankfurt.

'I've been experiencing this intermittent problem since October 2001 (when I purchased my A4 2.5TDi Quattro, engine code: AFB), and since then, almost ALL components of the drivetrain have been replaced: engine (2 times), transmission (3 times), clutch (3 times), drive shafts (1 time), driveshaft (2 times), ESP (3 times), turbocharger (3 times), rear differential, all hoses, pipes, electrical sensors, timing belt, engine control unit, water pump, and starter motor, not to mention the 7 mass airflow sensors I've gone through.'

Conclusion: The error is still present, and the Audi engineers, specifically those from the IN department, are at a loss (they are aware of the problem, it is reproducible, but cannot be fixed) and are not offering any further solutions.

For me, that means either learning to live with the problem or selling the car.

By the way, in my opinion, the jerking is caused by a dual-mass flywheel that is undersized.
With even a slightly higher amount of power/torque than the engine is actually designed for (150 hp, 310 Nm), the effectiveness of the dual-mass flywheel is no longer sufficient, and the vibrations that occur during acceleration in EVERY gear, but are usually only strongly noticeable in higher gears (4th, 5th, and 6th), where the engine speed slowly increases, cannot be fully absorbed.

And here's something else funny: please let the engine idle slowly, increasing the RPM to 1400-1800 (depending on the temperature); somewhere within that range, a strong vibration starts. The cause? According to Audi, it's unknown. The solution? There isn't one. Whoever finds the cause will also have the solution to the vibration problem in this thread.

Stefan.

Axo, valve cover gasket: forget about getting it to seal properly.

That definitely won't work. Despite several constructive modifications, every euro spent would be better off used to buy beer instead of being invested in further sealing measures.

Either they are leaking from the nozzles or from the contact surface; a solution is not currently available due to a production defect.

Stefan.

(He's still an Audi fan, despite being utterly desperate.)

Ah, now the information is starting to trickle in.

But we both have a Tiptronic transmission, Stefan!

How have you been driving it on the Autobahn since 2001?

Hello GarfieldMZ!

How are you going to proceed from here?

Hello ,

Have you ever disconnected the AGR (Abgasrückführung)?
@ Dennis, is the strut from the turbo causing this (wasn't it working fine before without any jerking or issues)?
-> I think we don't need to talk about oil leaks... or have you already replaced the KGE (Kurbelgehäuseentlüftungsgerät)?

Best regards, Manuel.

...so, I've been through all of this before!

AGR is disconnected (metal plate), KGE is new, VTG is working perfectly.

Hello everyone,

Today, we picked up the A6 again. During the short test drive, the jerking was no longer reproducible. We then drove a longer distance on the highway. During that time, it started to jerk again, although only for a short period and not with the same intensity as at the beginning, but it was definitely still there, or rather, it reappeared.
Okay, here's the translation:

'I now have two theories. Either the problem resolved itself during the workshop visit, or the initial replacement was already fundamentally correct. Ultimately, he now has a new mass airflow sensor (MAF), which eliminated the black smoke during the misfire, but not the misfire itself. Then, the diesel filter, the NOx sensor (NOx sensor), and another injector were also replaced.'

Okay, I've just checked the values. The air mass has increased from 680 to around 780, which I still consider to be too low. For that reason, I'm going to disconnect the EGR valve. The idle speed control shows that even with the air conditioning on and the gear engaged, two injectors are still showing values of +2.5 to occasionally +4.
Möglicherweise sind noch mehr Düsen defekt...
The displayed torque from the Tiptronic oddly doesn't exceed 290 Nm. I have no idea if this value is even reliable!

@Knubbi: As I mentioned before, I'm going to temporarily disconnect the AGR (Abgasrückführung) and also take another look at the linkage. Let's see if I can find anything else...

@Manuel: The KGE (likely referring to a specific component) is working correctly on this one. Hopefully, mine will be replaced next week. Were you planning to try the conversion to the Cyclone separator?


Regards,

DENNIS

What exactly has been changed now?