Slight jerking/stuttering between 3000 and 4000 RPM - Help!!!

Hi everyone,

I hope you can help me. I've used the search function and read through the entire collection, but I haven't found a solution to my problem.

I'm having the following problem:

On my Audi A6 2.5 TDI, model C4, manufactured in 1996, with engine code AEL, the mass airflow sensor was defective. Error description: Mass airflow sensor - short circuit, open circuit to ground.

When that was the case, it logically meant he had no more power. I had the mass airflow sensor replaced by a certified mechanic two weeks ago. So far, so good, the power was back to normal, but I then experienced a slight hesitation between 3000 and 4000 RPM when accelerating. 'This jerking occurs whenever the engine is cold, but the longer you drive, the further back in the RPM range the jerking shifts, until it eventually disappears completely after about 30-45 minutes.'

Following that, I had the error memory read again, and one error was detected: 'Mass airflow sensor - short circuit, interruption after positive voltage!!' I was given a new appointment to replace the mass airflow sensor again. Until that appointment, the warning light for the engine electronics would occasionally illuminate for 2 minutes. I had experienced something similar about a year ago in the summer when it was very hot in the car, and I immediately turned the air conditioning on full blast after starting the engine. However, at that time, there were no noticeable jolts or anything like that when the warning light came on. That happened again on that day, and I didn't think much of it because it had happened before and then never again.

Okay, so I went back to the friendly mechanic to have the mass airflow sensor (MAF sensor) replaced again. However, because the engine control unit (ECU) had lit up, the throttle position sensor had stored an error code. The mechanic now suddenly blamed the throttle position sensor for everything, which I didn't believe, especially since it also costs 200 euros and there were no issues with it last year. Consequently, the MAF sensor wasn't replaced, but only the error code was cleared, and I was told to drive it again.

Okay, so I did that, but the misfire was still there, and the mass airflow sensor (MAF) was showing an error again (intermittent fault after ignition!). So, the MAF sensor was replaced again. When I drove out of the workshop, everything seemed fine, but that was misleading because the engine was still warm. This morning, when I got back in the car and drove, the misfire was back. The engine warning light hadn't illuminated yet. I don't know if an error has been logged again, but I suspect the mass airflow sensor (MAF) is the culprit and is stored in the error memory.


Could it be that the needle lift injector is causing a false error, because the mass airflow sensor (MAF) always appears in the error memory?

Could the needle lift mechanism be the cause? I haven't done the compression test at 3000 RPM yet, using the screwdriver.

Does anyone else have a solution ready?

I'm not sure what could be causing it anymore, and I don't want to invest any more money unnecessarily, since Audis aren't exactly cheap.

I would be very grateful for any tips you can offer.

Once the problem is resolved, which I hope will happen soon, I will definitely post the solution.

Sure, here's the translation:

'MFG' is an abbreviation for 'Mit freundlichen Grüßen,' which translates to 'Sincerely' or 'Best regards' in English.

Me again.

Okay, so I tested the needle valve governor today, as described in this forum, by setting it to 3000 RPM and tapping it with the handle of a screwdriver. The engine speed did not drop when the knocking occurred, so I think we can rule out the needle valve lifter, right?

Then I removed my chip and replaced it with the original one to see if the problem was related to the chip. Even with the standard chip, he exhibits the same symptoms.

Then I installed my old mass airflow sensor, which results in significantly less power, and sure enough, the jerking between 3000 and 4000 RPM didn't occur. I can only explain it this way: the engine already has less power with the old mass airflow sensor, so it might not be much worse or experience any more jolts or fluctuations.
But I think the needle injection valve is probably ruled out, because if that were the problem, it would have caused the same issue with the old MAF sensor.

To clarify again, the jerking is like when the engine has its full power, and then suddenly the mass airflow sensor fails, similar to a loose connection. 'During the moments when it stutters, it only delivers as much power as it would with a faulty mass airflow sensor for 1-2 seconds, then it returns to full power, and then it drops again, etc.'

So, the jerking only occurs with the new LMM, when the engine is running at full power again. It's just funny that this is the second new LLM in two weeks.

To what extent could the wastegate valve or the EGR system be related to this?

Or could it also be one or more fuel injectors that are not injecting the required amount of fuel at that engine speed?

I would be grateful for any advice, and my wallet certainly would be too.

Hello!

I'd like to take a few trips using VAG COM. Log air mass data.

You can check the influence of the AGR valve using a small piece of metal and two gaskets. (This will completely seal it off from the intake manifold).

One more question: Is the stuttering gone when the engine is under full load? What is the performance like (without a chip)?

Regards,

Knubbi.

Okay, as far as I know, my A6, manufactured in 01/96, doesn't have a COM interface yet. He only has the normal error codes, otherwise I think Audi would have already tried something to fix it, especially since he's already been to the workshop three times for this issue.

With the stock chip, it has its normal, standard performance, but as I said, the jerking is still present. It occurs when the engine is cold, around 2800 RPM, but the longer I drive, for example, for an hour, and I occasionally rev the engine higher, like on the highway, the jerking shifts to higher RPMs, until it eventually disappears. As I said, it takes time.

I've rarely noticed this issue in the city, as I usually shift gears before 3000 RPM. It only happens when I accelerate more aggressively and rev the engine higher. From idle up to approximately 3000 RPM, everything is normal; there's no hesitation or jerking.

So, I can't explain it, but I haven't heard of or read about such a problem myself .

Hello,

No, the AEL should definitely have some readable and informative measurement value blocks.
If the workshop hasn't yet performed a test drive with a diagnostic system, it's more likely that they're waiting to see if the customer will leave more money behind, rather than that they're unable to access diagnostic data.
Well, or maybe they didn't do it because they can't interpret the values anyway...
-> Alternative workshop.

Best regards, Rainer.

Rainer K. wrote:

Hello, No, the AEL should definitely have some readable and informative measurement value blocks. If the workshop hasn't yet performed a test drive with a diagnostic system, it's more likely that they're waiting to see if the customer will leave more money behind, rather than that they're unable to access diagnostic data. Well, or maybe they didn't do it because they can't interpret the values anyway... -> Alternative workshop. Greetings, Rainer

Okay. Of course, a VAG-Com can be used for that.

It looks like there might be a cable problem. By the way, the air mass sensor on this model rarely breaks.

Okay, I'm happy to be proven wrong, so I'll try using the VAG-Com at the Audi dealership tomorrow.

I don't think it's a cable problem, because it always happens within the same RPM range and then disappears after a while of driving.

Could it possibly be a faulty boost pressure limiting valve?

Or a relay?

I might consider deactivating the AGR (Abgasrückführung) system to see if it makes a difference, although I'm not really sure it will.

Hi everyone,

Okay, to revisit the topic, I was at Audi again today regarding the problem I described. They performed a diagnostic test using VAG-COM, and the workshop foreman said that all the values were within the normal range (boost pressure, mass airflow sensor, etc.). Unfortunately, I didn't get a printout of the results.

Okay, so during the test drive, an error was logged by the needle position sensor, and in addition, the mass airflow sensor (MAF) was again present in the error memory. The needle position sensor was replaced today, and I was told that if the needle position sensor malfunctions between 3000 and 4000 RPM, it could cause the MAF sensor to regulate incorrectly, which would then result in the MAF sensor constantly appearing in the error memory. That doesn't sound right to me. So, the needle position sensor was replaced, the error memory was cleared, and we went on a test drive. And I had to confirm again that it had a slight power drop in that RPM range, and that was on two attempts.

The funny thing is, whenever I restarted the engine 2-3 times, the problem would disappear, and there would be no more error codes in the system. I don't know if the outside temperatures are the reason why the shaking has stopped after about 10 minutes, or if the NBF actually made a difference.

When I mentioned the boost valve and the EGR as potential causes, I was told that if that were the case, it should then display the error code 'intake manifold pressure regulation difference.'

I don't know what to do anymore; I already have a bill of 850 Euros from Audi, and the problem is still there .

...or you might have an unstable power supply coming from the engine control unit... In my case (AHF with a faulty relay 109), the error memory contained some very strange entries.

What is relay 109 responsible for?

I already figured out what the relay does. However, the lines were actually checked by Audi, at least the ones related to the mass airflow sensor, etc.

Hi,

Current status as of today: Audi.

The needle movement sensor didn't help, and the error memory now shows 'mass airflow sensor (MAF) fault - short circuit' again!

'The fourth LMM (lambda sensor) has been ordered and will be replaced tomorrow. If that doesn't fix it, I'll cancel the whole thing and have the parts removed again! Now, the engine control unit (ECU) is also being considered, because, well, maybe... blah blah blah!' I'm fed up and I don't want to replace half the car!!!

It seems like not many people have any advice on the matter, well, even if the people at Audi can't find anything.

Sure, here's the translation:

'MFG' is an abbreviation for 'Mit freundlichen Grüßen,' which translates to 'Sincerely' or 'Best regards' in English.

That's enough now.

What else could it be besides the power supply from the control unit or the wiring to the mass airflow sensor?
There's no novel to be written about that, and if Heiner gets the fourth one at Audi... Instead of installing a mass airflow sensor, maybe they should try using their brains next time! They should probably search for a brain on eBay!

And if you're not even capable of trying to find the cause of a problem with your car, I wonder what the point of this entire thread is?

We are not here to chat, nor are we a free, on-demand repair shop assistance service!

And if you yourself are not capable of searching for the cause of a problem in your car, I wonder what the whole point of this thread is?


Great post!!

Sure, I'm as dumb as a rock, I smell like instant noodles, I don't have an ID, and I definitely don't know anything about cars! But luckily, the problem goes away when the wires heat up after about 15 minutes of driving. It's actually logical that it's a power supply issue because loose connections never cause problems sporadically; they always happen when I'm between 3000 and 4000 RPM, or faulty relays only malfunction for 15 minutes, then they give up and work perfectly fine afterward!

I don't actually see this thread as unnecessary, because it seems like this kind of problem hasn't occurred very often, or am I wrong? I didn't attack anyone, and that's so that not so many people have an opinion or comment on it, including you, if you feel attacked or have any problem whatsoever.

If it's unnecessary to present such a problem in a forum like this, I wonder what the purpose of the forum is in the first place.

And now, here it is, especially for you:

THE WIRING AND POWER SUPPLY HAVE BEEN CHECKED!!!

Even though you are a moderator here in this forum, I find your way of expressing yourself towards others, and the way you question the abilities of others, a bit excessive. SORRY!!! And besides, it's not like I've completely ignored your advice so far!

I'm still hoping to get some tips, but if not, I'll have to accept that.

What I wrote reflects my OPINION and should not be taken as an attack against you.

Sure, here's the translation:

'MFG' is an abbreviation for 'Mit freundlichen Grüßen,' which translates to 'Sincerely' or 'Best regards' in English.

Na na na! Do you think it's reasonable to completely berate someone who wanted to help you? I don't. Save your further comments.

I've been following this thread, and I have to say, it's impossible for me to believe that 4, that's four, LLMs would have entered the eternal hunting grounds without a reason. Just think about it. I wouldn't go to that Audi workshop anymore. They seem to be really clueless.

Regarding the reported error, I can easily imagine a loose connection or similar issue that only occurs within a certain speed range due to certain vibrations, and which might disappear with increasing temperature. It doesn't necessarily have to be a cable.

Perhaps the reported error is just a secondary symptom, and the underlying cause is insufficient boost pressure. Based on logical reasoning, the control unit then indicates: 'error: mass airflow sensor.'

What does your intake manifold look like? Is everything sealed properly? Is the boost pressure okay within that RPM range? Is the diesel fuel supply working correctly?

Even though you are a moderator here in this forum.

You're not quite right. You just argued with the boss; his name is Rainer, and he's the administrator. It is his forum.

But, what you have to be given credit for is that you actually read the technical articles. The conclusion was a bit slow, but okay. Therefore, we don't have to argue, do we?