Turbo Lag: Multiple Holes in 2nd Gear?

Hi!

Okay, I've noticed lately that when I fully accelerate in first gear (up to about 4000 RPM) and then shift into second gear while still keeping my foot completely on the gas!

It starts up fine, but I notice occasional brief stalls in the middle of the process, about 3 times before it returns to 4000 RPM.

Do you know what I mean? It's like I'm letting off the gas and then accelerating again. However, I always keep my foot consistently on the accelerator. But I only noticed this in second gear, not in any other gear.

I called them 'turbo holes' because I couldn't find a more suitable name.

What could be the reason for that?

Best regards, DG

P.S. Regarding the car: It's an Audi A4 B5, manufactured in 2000, with a 1.9 TDI engine, 115 horsepower (PD), and 48,000 kilometers on the odometer.

Hi!

Well, apparently no one here has any advice about my problem either! Even though you were recommended to me *G*.

Well, maybe someone out there knows something after all... it would be nice.

Best regards, DG

The sound of a surging acceleration suggests the common problem of a 'stuck variable geometry turbocharger (VGT),' and there's a technical article about it in the error database, along with numerous posts on the forum.
However, this shouldn't happen again at the AJM...

Hi,

If someone searches for "sudden acceleration" in a search engine, they will find a thread where the culprit was identified as the mass airflow sensor (MAF).

/viewtopic.php?t=2235&highlight=pumping acceleration

Hi!

I've read both of these articles and also searched the forum, but none of these explanations seem to apply to my problem. For example, it only happens in second gear, and it's not losing its maximum speed. I drove 220 km/h (according to the speedometer) on the highway yesterday, and everything was fine... so, in my opinion, it must be something else!

Best regards, DG

dg17 wrote:

...so, in my opinion, it must be due to something else!

Hi,

Looking for a brave soul.
It's always important to use a diagnostic tool when performing such a search.

Hi,

If a diagnostic tool isn't available, I would at least try using an LDA (Linear Density Analyzer). In my opinion, an LDA is essential equipment for every TDI engine.
This allows you to at least check the pressure build-up and its progression.
I experienced similar problems with surging acceleration, also in 3rd gear. The diagnostic tool (LDA) confirmed that there was an issue with the turbocharger pressure regulation. When reaching 1.2 bar, the boost pressure dropped to 0.6 bar and remained there for about 1.5 seconds before rising again, eventually settling around 0.9 bar (the LDA gauge needle jumped back and forth like a cuckoo clock pendulum). In my case, it turned out to be the notorious stiff linkage between the vacuum sensor and the turbocharger.
In the lower sections, the control system needs to be able to react much faster, which isn't always possible with a jerky adjustment mechanism.
Well, I hope you figure out the problem.