AXR Lagging? Troubleshooting Guide & Fixes.

Hi everyone!

Okay, to summarize: On my Golf IV TDI PD, manufactured in 08/01, with 57,850 km, I noticed that it runs very unevenly at idle when it's warm. I took it to the dealer, and after several attempts and reading the diagnostic data, they determined that one PD element was at 1.5 mg/h. Consequently, all the PD elements were replaced. This didn't fix the problem; it still vibrates. Then, the engine control unit (ECU) was replaced, which resulted in the vibration becoming significantly weaker and now only occurs sporadically and with varying intensity. Until yesterday, it manifested as a 'wobbling,' but today it was worse again, with a noticeable vibration.

What should I do next? What tests should I have done? What could be causing this annoying idling problem? Please help me; I'm going to the dealership again tomorrow afternoon.

Best regards,
VipViper2000

P.S.: If you want more information, just let me know. And if you're wondering why I'm not using the search function, I can only say that both the PD elements and the engine control unit have already been replaced.

Hmm, the function of the EGR valve needs to be checked thoroughly. It might be clogged with soot and oil, which could be preventing it from working properly.

So, if you're referring to AGR as a cruise control system (Automatic Speed Regulation System, so you know where I'm coming from), I'm afraid I have to disappoint you, because I don't have one at all.

No, GRA stands for 'Geschwindigkeitsregelanlage,' which translates to 'speed control system.' AGR stands for 'Abgasrückführung,' which translates to 'exhaust gas recirculation.'

Exhaust gas recirculation (EGR) refers to the process of redirecting exhaust gases back into the combustion chamber. This is done to reduce combustion temperatures and the concentration of nitrogen oxides.

Best regards, WarLord.

Oh, okay, so I misunderstood. Well, I'll definitely tell the nice person about it tomorrow. How did you come to that conclusion? And what else could it be due to?
I'm sorry if I seem impatient, but I'm just at a loss and don't know what to do next.

The good old LMM (likely referring to a specific product or component) might also be a possibility; you could try swapping it out as a test.

Sorry, but the LMM (likely referring to a lambda sensor or similar component) has already been replaced. It was replaced right at the beginning, about 5 months ago.

We recently had an A4 with an AVF engine that also exhibited noticeable vibrations.
It's important to note that when you revved the engine while it was idling and then let it return to idle, it would often jerk or shudder quite violently for about 10-20 seconds. Afterward, the jerking would lessen, but it would still be noticeable.

After everything has been checked and done, we found it.

'I replaced the catalytic converter, and then it was gone... which is strange because there was nothing visible or audible coming from the catalytic converter, neither when it was installed nor when it was removed.'

Maybe this will help you...

Hi everyone!

The frustrating thing is that I can't check it myself and I always have to rely on the people from the workshop. And, as you said:

...which was strange because there was nothing to see or hear on the CAT, neither incoming nor outgoing.

I can't just have all the parts replaced simply because there's even the slightest suspicion, right? How did you come up with the idea about the catalytic converter?

Best regards,
VipViper2000

Well, we don't have a crystal ball here either. What do you want then? Should we repair your car for free? Oh my...

Okay, we observed what happened when the car was shaken. For example, the exhaust pipe vibrated. Then we lifted it up and looked further forward. We noticed that the vibration was causing... oh wow, the exhaust pipe was vibrating much more. I put on a glove and held the exhaust pipe in place... hmm, it's better, but the vibration hasn't completely disappeared.

Then I took a pipe and pressed it against the muffler, but there was hardly any change.
Okay, so I started at the front with the flexible pipe... hmm, it didn't vibrate as much as the ESD... hmm, what's in between... I used the catalytic converter pipe and twisted/wedged the catalytic converter slightly... oh, no more vibration, I tried it 10 times, nothing... I loosened the blockage... VIBRATION!!!

I thought about it for a long time, could it really be? Since we couldn't think of any other solution, and all the measurable values from the control unit were perfectly within the normal range, we installed a new one... and it was gone.

That wasn't my intention. You also don't know the background. It wasn't just the problem with the jerking; I've also already had the third battery installed because the thing was constantly draining and nothing could be found. Additionally, I always had the problem that the RPM would suddenly jump from 1600 to 2400 in 4th gear and then slowly decrease again – my suspicion was a faulty clutch. However, the error cannot be reproduced and hasn't occurred for a long time.

I've only had the car for just under six months, and it has a one-year used car warranty, which I intend to use to fix all the problems. I've been to the workshop so many times that I've stopped counting.

Okay, the issue with the KAT (presumably a specific system or component) is a bit different for me. Unfortunately, I can't reproduce the jerking behavior as consistently as you describe. For me, it sometimes doesn't jerk at all when idling, and then suddenly it jerks quite strongly. However, I can't identify any pattern, for example, that it only jerks when a gear is engaged or when it's outside (presumably referring to temperature or environment).

Hi VipViper2000,

'Often, with a defective catalytic converter, the monolith can become dislodged from its position and end up lying sideways inside the converter, causing a buildup of exhaust gases. Tap on it; if it sounds hollow, that's likely the problem. You can also identify issues in the exhaust system by checking the duty cycle of the magnetic valve for the variable turbine geometry (VTG). In the case of a blocked exhaust path, the duty cycle will be higher than normal.'

Okay, I'll definitely mention it to the workshop tomorrow, and maybe even tap on the catalytic converter. But they should really come up with that idea on their own.

Errors in the exhaust system can also be identified by examining the duty cycle of the magnetic valve for the VTG (Variable Turbine Geometry). In the case of a blocked exhaust path, the duty cycle will be higher than normal.


I'm sorry, but could you explain that a little more? What is a 'Tasverhältnis,' and what does 'VTG' mean?