G4 ALH: Pumping Loss Acceleration Problem

Hello fellow mechanics.

My Golf IV, manufactured in 2000, with an ALH engine and 106,000 km on the odometer, is exhibiting a strange behavior.
Exhibits acceleration behavior.
The car pulls relatively smoothly in the first, second, and third gears.
When accelerating in 4th and 5th gear at full throttle, the car starts to 'pump,' meaning...
It takes about 2-3 seconds to load normally, then the loading speed drops drastically. Immediately after that, the game restarts from the beginning. It's like I'm constantly...
'accelerate to full speed and then ease off the accelerator shortly after.'
The acceleration continues up to approximately 160 km/h, after which it stops.

- I have already flushed the LMM with brake cleaner.
- The VTG (vehicle traction generator) can still be moved manually, to the extent possible.
- The air filter is new.
- The engine is sputtering and not running smoothly.

Any help is welcome!

Hi Marco,

Have you already investigated the tax pneumatic system? (Referring to a technical article?) Do you keep your foot on the accelerator pedal constantly when this problem occurs?

Best regards, Christian.

Hello haehnlein,

I have already read the article, and yes, I always keep my foot on the accelerator. This acceleration behavior is especially noticeable during overtaking maneuvers.
It was quite embarrassing, as I had to find out!

hello Marco,
Cleaning the LMM *can* improve things, but it *doesn't necessarily* have to.
I also cleaned my faulty mass airflow sensor, but it didn't help, which isn't surprising since it was already perfectly clean.
I'd like to borrow a mass airflow sensor (MAF) from an acquaintance for a test drive. The symptoms I experienced with my faulty MAF were the same: wavy acceleration and the inability to reach the top speed.

Marco wrote:

When accelerating in 4th and 5th gear at full throttle, the car starts to "pump," meaning... He usually takes about 2-3 seconds, then it drops drastically. Immediately after that, the game starts again from the beginning.

Hi Marco,

I suspect, like Alois, that there's a problem with the LMM (likely a faulty LMM sensor).

It would be interesting to log the air mass measurement group here, if you can access VAGCOM.

My G4 with the 110hp engine had the same symptoms. Cleaning the mass airflow sensor (MAF) didn't help, but replacing it fixed the problem. Now, the engine feels like it's pulling much better.
Regards,
Erwin.

Hello fellow enthusiasts,

I also re-checked all the hoses and the coolant reservoir for oil leaks and any signs of leakage, but everything seemed to be fine.
Since I still have a used car warranty, I will be using it next Tuesday. Hopefully, they will let me.
'Could you please check the error memory?'
Of course, I could have just done it right away, but my strong urge to tinker and customize wouldn't allow it.
Once the car is back from the repair shop, I'll give it another try.
File a report.

Hello fellow mechanics.

Bullseye!!! 'Intake manifold pressure control differential.' It was the mass airflow sensor. I had them give me the defective one.
I will try to carefully break it down into its individual components.
Let's see what mysterious thing has broken down in the LMM.
If you are interested in seeing photos of the interior, please post a comment here.

Hello,

I don't understand how a faulty mass airflow sensor (MAF) could cause a difference in the boost pressure regulation. Aside from the possibility of too low boost pressure due to insufficient fuel injection caused by low MAF sensor readings, that would then be a bug in the engine control unit (ECU).
Since I don't expect that to be the cause, even if the "pumping effect" disappears after replacing the mass airflow sensor, there might still be an underlying issue with the turbocharger pressure control.
In other words, if the emergency program is activated again when accelerating strongly in the near future, the error is most likely "throttle pressure regulation difference."

Best regards, Rainer.

@ Rainer

Im Fehlerspeicher jedenfalls war laut VAG der o.g. Error logged.
After a test run, it was decided to replace the mass flow meter.
Subjectively speaking, the problem seems to be gone, and the car is pulling well again.
And the top speed will be reached relatively quickly, as far as an unmodified ALH engine allows. We'll see if there's anything more to discover.