Weird issue, two different cars same symptoms!

[Mullz]

Ok, bit of a long one but it's super weird. This has happened in both a 2006 VW Passat DSG and my 2008 A4 Avant B8.

Randomly when driving it's nice and smooth and then something kicks in and changes the the exhaust tone like deeper. The revs then become ever so slightly wobbly, for instance in the B8 doing 30 it suggests shifting into 4th. When this issue kicks in it it suggests I go back down to 3rd and only suggests 4th when up to 33/34mph.

When this issue happens, even when the engine is cold, if I pull over and kill the engine the fans are going full pelt. If I then start the engine again, fans stop and problem resolved.

No error codes or engine lights.

Any ideas or things I can test?

My old passat did it lots and it's the reason I got rid of the car as I thought it might be the turbo and the car wasn't really worth it, now I've got this one, same ruddy thing has happened albeit on a couple of times in a month.

Cheers

David

Edited March 18, 2022 by Mullz

[Stevey Y]

17 minutes ago, Mullz said:

Ok, bit of a long one but it's super weird. This has happened in both a 2006 VW Passat DSG and my 2008 A4 Avant B8.

Randomly when driving it's nice and smooth and then something kicks in and changes the the exhaust tone like deeper. The revs then become ever so slightly wobbly, for instance in the B8 doing 30 it suggests shifting into 4th. When this issue kicks in it it suggests I go back down to 3rd and only suggests 4th when up to 33/34mph.

When this issue happens, even when the engine is cold, if I pull over and kill the engine the fans are going full pelt. If I then start the engine again, fans stop and problem resolved.

No error codes or engine lights.

Any ideas or things I can test?

My old passat did it lots and it's the reason I got rid of the car as I thought it might be the turbo and the car wasn't really worth it, now I've got this one, same ruddy thing has happened albeit on a couple of times in a month.

Cheers

David

Hi sounds like they are both diesels and trying to regenerate the DPF, the reason for the suggested down shift  is to raise the revs to help with the regeneration process by increasing engine temperature.

Steve.

[Mullz]

So it's a common thing or does it suggest the dpf needs cleaning? The VW got real bad and the noise became very noticeable as well as one time after driving quite a distance with it like it, pulling over and smoke was coming from behind the engine. Not had that with the Audi but scared it might get worse if it's something I need to look at.

Cheers Steve for the response, again 😄

[Stevey Y]

4 minutes ago, Mullz said:

So it's a common thing or does it suggest the dpf needs cleaning? The VW got real bad and the noise became very noticeable as well as one time after driving quite a distance with it like it, pulling over and smoke was coming from behind the engine. Not had that with the Audi but scared it might get worse if it's something I need to look at.

Cheers Steve for the response, again 😄

Hi its a universal thing with diesels they all do it especially when treated to lots of short journeys at low speeds, best thing to do is fill it with decent quality fuel and give it a run down the motorway for about twenty miles that will clean most of the crud out, then buy a fuel additive suggest Hydra Maximus I use it in my cab which does a lot of short journeys but because the additive makes the fuel burn more efficiently the regenerations are less aggressive and not as frequent, also stay away from supermarket fuel IT WILL KILL YOUR ENGINE, do not keep stopping when the fans come on as this is known as a aborted regeneration which over time will cause engine/emission system failure.

Steve.

Steve.