2.5 TDI Problems: Common Issues & Solutions

Hello,

I hope that I am in the right place in this forum . You can see that by the number of my posts.

I simply don't know what else to do. And the worst part is that several VW dealerships have also failed because of it.

V6 TDI 4Motion, 28,000 km, manufactured in December 2001.

Sure, please provide the text you would like me to translate from German to English.
1st gear -> Accelerate to approximately 3,500 RPM -> Release the accelerator pedal -> A sound that I can't replicate. Something like the feeling of having chewing gum stuck in your throat and trying to force it back in with a sigh. No, my car doesn't have chewing gum in it!

In addition to that, when driving on the highway: a constant 2000 RPM, but when you press the accelerator, it jerks violently 1-2 times, as if there's no fuel being delivered.

Simple acceleration in 2nd gear: 1,500 RPM -> around 2,000 RPM, there's no jerk and better acceleration.

Is there anyone here who has any other ideas besides going to get some chewing gum?

Thank you in advance.

--Gustaf

Hello,

Is your car a Passat with the engine code AKN?

Do you have any data from the workshops (e.g., error code readouts, measurement logs, etc.)?

Hi,

Sorry, I forgot .

Passat / Engine code: AKN.

The error memory shows no problems except for 3 Climatronic-related errors.

Regards,
Gustaf.

gustaf wrote:

Sure, please provide the text you would like me to translate from German to English. 1st gear -> Accelerate to approximately 3,500 RPM -> release the accelerator => a sound that I can't describe. Something like the feeling of having chewing gum stuck in your throat and trying to push it back in with a sigh. No, my car doesn't have chewing gum in it!

Hi,

AFAIK, the AFN (81kW TDI) engine has an alternator with a freewheel clutch that can make similar noises, and the AKN engine might have one as well.
(Just an idea).

Best regards,
Munch.

Hello,

Simple acceleration in 2nd gear: 1,500 RPM -> around 2,000 RPM, there's no jerk and better acceleration.

--Gustaf

Hello Gustaf!

'I have an AFB V6 TDi, but I also experience that slight jerk. You can feel it in 3rd gear as well, at a similar RPM. I've asked a few people from what are supposed to be 'specialized workshops,' but they all came to the conclusion: 'We have no idea what you're talking about, it must be normal...'

I would also be interested in the cause of the jerk, but after 18 months, I gave up trying to find it. One possible cause I considered was a potentially slow or sluggish boost pressure regulation. According to VAG-COM, there is also what I consider to be a quite significant 'overshoot' in boost pressure at the moment of the jerk.

Regards,
DENNIS

Hello,

I think I have the same problem.

It's related to the turbocharger. I think it might be the electronic control system (the vacuum hoses are okay) or the variable geometry turbine vanes.
It seems that the paddles are positioned 'too close' together at lower RPMs, which creates a lot of pressure quickly but 'chokes' the engine.

At high speeds, the boost control system activates, removing the restriction and resulting in a 'kick' and faster acceleration.

The noise you hear when reducing throttle is the turbo reaching its 'stall speed.'

I'm going to try to shorten the actuator's travel path on my car. (When you start the car and look at the actuator, you can see it moving.)

I hope this is clear enough, as my German isn't perfect.

Hi,
I think that's understandable. In the opposite case, most forum members, like myself, would probably have to switch completely to English.
Here, I would like to translate the word "Stall" as "flow separation." It can be noisy and also occurs in the specific variant called "rotating stall," where the rotational speed is significantly lower than the rotor speed. It normally only occurs in compressors, but in this case, it is likely caused by the turbine because when the gas flow is reduced, the variable geometry vanes (VTG) cannot close quickly enough, causing the blades to be impacted at too large an angle.

I'm going to try to shorten the actuator's travel path on my car. (When you start the car and look at the actuator, you can see it moving.)

I hope this is clear enough, my German isn't super.

Hi dogde_cummins,

'The 'actuator' likely refers to the linkage between the turbocharger and its vacuum actuator. It's normal for this linkage to move when the engine is started. At idle, the guide vanes of the turbocharger are set to their maximum position (the linkage points towards the vacuum actuator). If you shorten the linkage, it will only get worse because the turbocharger (depending on how much you shorten the linkage) will reach and exceed its target boost pressure much earlier. Please check the control valve that mixes the intake air with the exhaust gases from the EGR system. This valve is located in the hose connection between the intercooler and the intake manifold. For example, on an Audi A4 V6 TDI, the valve is located directly in front of the left headlight (from the driver's perspective).'

Hello everyone,

Thank you for your contributions.

I adjusted the blade position slightly last weekend, and the problem seems to have been resolved.

Thank you for your contributions. I should have taken a picture, but I didn't have my camera with me.

Okay, so here's the thing; (remember, I have AFB V6).

When the engine is started, the control rod is pulled upwards (creating a vacuum) until it reaches the (adjustable!) stop. We are still talking about the idle speed here. This is the maximum blade adjustment. It is this stop that needs to be adjusted. It becomes easier if you loosen one of the bolts on the vacuum actuator (which is held in place with two bolts) and push the actuator forward.

I turned the screw (size 9 key for loosening the 'retainer' screw and small Allen key) approximately half a turn clockwise (it only needs a very small amount) to tighten it.
It only takes a very small adjustment to fix the problem (at least my problem...). If you turn it too much, you'll notice that the turbo boost decreases slightly at low RPMs (starting at 1300 RPM), and that's not what you want. So, be patient and try a few times.

By the way, I sprayed a little Teflon spray into the control valve... The control system is working well, and I don't think it had anything to do with the turbo.

I hope I've made a valuable contribution.