2.0 TDI Shakes: Common Rail Issues & Solutions

Hello TDI specialists!

I have a new A4 2.0 TDI CR (143 hp), 6-speed, and recently I've been experiencing this peculiar problem:

The car repeatedly jerks when accelerating, and occasionally also when coasting (with engine shut-off). This manifests as two short, gentle jolts during acceleration, and a single, mild jolt sporadically while coasting.

It's temperature-independent and occurs virtually in EVERY speed range. You only don't feel it as much below 2000 RPM because the problem is dampened by the dual-mass flywheel (ZMS) when driving in a high gear. But fundamentally, it's ALWAYS there, regardless of which gear you're in and what engine speed.

The problem almost always occurs when you're coasting (i.e., driving without pressing the accelerator) and then suddenly press the gas pedal. And now there's another effect that is 100% related and might be helpful in troubleshooting. The car occasionally jerks, even while coasting (without using the accelerator). This jerk can only come from the gas pedal, right?
However, what speaks against the accelerator pedal is that I also tried to reproduce the problem while the car was stationary. By manipulating the accelerator pedal precisely at the point where the engine starts to respond (the "sweet spot"), I couldn't replicate the issue. Unfortunately, I can't reproduce it when the car is not moving, and the idle speed is perfectly stable!

Which component could be sending a signal that causes the engine to briefly "jerk" or "surge" even when thrust is supposed to be cut off? The actual fault must be located there!

Please provide helpful information before I confront my friend with this.

I would also appreciate it if someone could tell me which materials to use for a logging project. I can then share the results afterwards.
So far, nothing has been stored in the memory. Perhaps the problem is not yet pronounced enough?

Otherwise, the car runs completely normally. It's a very strange situation!

Thank you all.

Greetings.

Oh my god, I've really gotten myself into a mess. If none of you experts have any advice, I'm worried that the dealership will seriously find something wrong with it. It's good that the car only has 6900 km on it. And if the dealership doesn't find anything, they are legally obligated to either fix it or allow me to return the car after three unsuccessful repair attempts, which is called "rescission." I will provide him with information about my legal rights.

Hello everyone.

Hello there!
It seems most logical to first present the problem to your car's master technician and have them accompany you on a test drive so they can identify the issue themselves.
I understand that the car is still under warranty. Any reputable dealership will take care of it.
Avoid telling him where to look; avoid legal discussions. After the troubleshooting is complete, ask for an explanation of what was done. Keep a copy of the order. If the problem cannot be resolved, request that the issue be escalated to the Customer Care Center. It's possible that a representative from the factory will get involved. Again, let them resolve the problem. The most important thing is that your complaint is documented in writing before the warranty/guarantee period expires. However, you don't need to mention that right now.
Here's what you can do yourself: With VCDS, you can read the control units for the engine and possibly the chassis (ESP) and record data during drives when the jolting occurs. You might find some anomalies there. Unfortunately, I can't offer any more specific advice regarding the engine due to my lack of experience with it.
And remember, the records and discussions about them belong here in the forum, not in the "Friendly" section.
Sure, here is the translation of the text from German to English:

"vg" translates to "very good" in English.
Herbert.

Hello!

Thank you for your reply so far.

I am absolutely certain that this is the path I must take, and I understand that now. I'm asking here only because I like to bring every tip with me when I visit the service center. Why? Because I've already been there, he recognized the problem even while I was a passenger, and he was completely unaware of it. I have an appointment scheduled, but unfortunately not until October. What he knows so far is that there are no error codes in the system and there isn't a current software update available for the control module (MSG).

"I enjoy doing diagnostic drives, but I would need to be told WHICH specific data points to log. My initial suspicion is towards the throttle valve, swirl flaps, EGR system, and DPF. The problem only occurs when transitioning from coasting to acceleration. If the engine is already under load (even during constant speed), and you apply more gas, the problem doesn't occur. It only happens when going from coasting to applying the accelerator, and that happens every time, at any RPM! Sometimes there's also a slight jerk while coasting, but it's rare and subtle."

What does "still under warranty" mean? I bought the car new just in June!

Kann mir wer bitte Tip's für Logfahrten geben? Das Gaspedal muß dabei sein, daß man sieht wann man aufs Gas geht. Aber was noch? Luftmasse? DrSure, here is the translation of the text from German to English:

"What are you doing?" "I'm just browsing." "Are you looking for anything in particular?" "No, I'm just window shopping." "Okay, well have a good time." "You too."

Thank you.

Greetings.

That initially suggests a simple software error, which I would expect to see when...
would not want to rule out the vehicle/engine combination either.
without having data from the MSG.

"So, that rattling sound in the drawer sounds interesting."
If this jerking only occurs immediately after a negative load change (LC), then...
It could be due to a combination of factors related to the ASD (Anti-Sway Device), which consists of a guide former... dc.
and the noise filter (…rf) and the dual-mass flywheel (DMF) that are installed in your car.

ASD is permanently installed and there are no options for modification or adaptation (as far as I know).

The vibration damper requires a rigid and stable powertrain with the given specifications.
Flexibility/stiffness. Subsequently, the natural frequency plus damping of the powertrain is determined for each gear, and also the "shape of the torque build-up" is analyzed.
(naturally in combination with various driver preference moments, key functionalities, etc.)
If you feel a jolt after a certain amount of time while already in gear, it could be due to momentary intervention from the ESP, MSR, or ASR systems (since you have an automatic transmission, there wouldn't be any momentary intervention from the gearbox) => this is less likely.
or it may be related to the activation/deactivation of auxiliary components (such as the air conditioning system, which likely has a soft start feature in your car's year of manufacture, making it barely noticeable), or possibly the generator (although I doubt that).

Would the MSG (Message Signal) disappear after a defined time (approximately 3 seconds) following thrust detection?
Requesting APP activation (I once had a case in RGN where it was incorrectly activated and causing torque-related issues with the PoI2), triggers an MOF (Monitoring) alert, and you're in trouble.
Error log entry. But you don't have one.

I've experienced this phenomenon several times during positive load tests: it feels like something in the powertrain needs to "engage" or "unlock" first (it only takes a few tenths of a second), and then it becomes more stable.
"A clutch was present, but it was usually a dual-mass flywheel (DMF) with outdated specifications."

Here are a few random thoughts...

Perhaps you now understand better why I asked about the existence of a timing chain tensioner (TCT) in the current 1.2 TSI engines a few posts ago.
"If it's not there, it can't break!"

Hi!

Okay, so that slight jerk during acceleration never happens immediately after releasing the gas pedal, but rather a few seconds later, and it's only very rare. It doesn't matter which gear you're in. Mechanically, everything seems to be fine, including the dual-mass flywheel (ZMS) and related components.

The actual jerking (two soft jolts with a slight throttle delay) always occurs when transitioning from acceleration to throttle. It doesn't matter if you quickly press the accelerator or very slowly depress it. This happens in every RPM range! It's like the engine momentarily stutters and then responds. It also doesn't matter if you continue accelerating or maintain a constant throttle position. The moment the engine changes load, meaning from zero throttle to even a little bit of throttle or a lot, it takes the throttle input with a delay, causing two short, soft jolts. If you keep your foot on the accelerator and never completely release it, there is no jerking.

It seems like some component is reacting too slowly when I accelerate. Could it be the throttle valve, the swirl flaps, or the EGR system?
At first, I thought it might be the accelerator pedal, because it's essentially only at one position – the very beginning of its travel. But when the car is stationary, I can't reproduce the problem, even with sudden acceleration and holding the pedal in that initial position. If there was a problem with the accelerator potentiometer, wouldn't it cause issues here too?!?!?

Greetings.

Small tip...

Okay, try disabling the AGR valve. Even if there's an error message (which you should be able to clear), you should notice a change in how the engine responds.

My AXR had this issue once as well. When the EGR valve was closed, it stopped happening. Afterwards, the TCU (Transmission Control Unit) software was updated, and the problem was also resolved with the EGR valve active }.

Danke! Great tip!

If I knew how it's done. How is it done on the new 2.0 TDI CR?

"However, according to the technician, there is definitely no new software available for this engine at the moment."

Greetings.

The 2.0 CR engine has an electric EGR valve, which means you only need to disconnect the connector from the EGR valve.
and then it's definitely permanently closed (unless it's left open).
=> I don't think so!).
During the exercise, there is a very high probability that the diagnostic light will turn on.
Alternatively, there's an FSP entry. Only do the exercise if you have your laptop.
within reach.

Good luck!

PD90

Okay, thanks, I was thinking the same thing because the 2.0 CR has the EGR valve directly after the throttle body and there's a connector attached to it. But why "within reach"? Couldn't I just delete the error code myself at home later? Would you notice that there was an error code that was deleted by someone?

Greetings.

Deleted is deleted... at least for the nice guy.

I just don't want to confuse him further when he starts troubleshooting in 2 weeks. Then, if he encounters something related to the error, he might start looking in the wrong place, and it might not even be the actual problem .

Greetings.

If the FSP is currently empty (as I understand from a previous post of yours), then...
and leave a comment on your "AGR & Co. exercises".
=> Simply delete it after you're finished.
Thus, you have restored the original state, and your workshop will be...
(hopefully) not be left in the dark about it.

When I say "within reach," I mean that depending on the software version and manufacturer, there are different replacement responses to FSP entries.
Sure, please provide the text you would like me to translate from German to English. I will only provide the translation without any explanations.
1) Only the workshop lamp/MIL is activated => not ideal, but harmless.
2) Engine protection level 1: Turbocharger remains active, EGR valve closed, speed reduction only through the engine control unit (RKF).
3) Motor protection level 2 - with adjustable torque limit for fault conditions (noticeably reduced).
4) Motor protection level 3 - with own torque limitation for very critical error scenarios.
(It is usually no longer possible to simply follow the flow of traffic.)

When does each replacement reaction become active? When does the workshop lamp turn on? And when is the error related to emissions (MIL)?
It now fills volumes and occupies entire departments (thankfully ).

=> I personally always take my computer with me when I go on a "diagnostic trip," especially for recording files and related things.

I would actually like to do a diagnostic test myself. However, I'm not sure which diagnostic tools I should use to get meaningful information.

By the way, the electronic throttle isn't the cause. I tried it with cruise control, and it still jerks. So, the accelerator pedal (and therefore the potentiometer) is probably not the problem.

Greetings.