Temperature-Related Stuttering?

Hello professionals!

After it has gotten noticeably colder again recently, a phenomenon has resurfaced on my TDI that had been dormant throughout the summer.
My A3 tends to experience occasional jerking or hesitation at low engine speeds, specifically within a narrow range of approximately 1350 to 1400 RPM, and under light load, especially when the outside temperature is low.
When driving through the city in 4th gear, you often find yourself operating within that specific RPM range, and you're naturally putting very little load on the engine.

I have, of course, read the relevant article, but I don't believe it applies to my pump.

Rainer wrote:

Quote:

At an idle speed of 900 rpm, an injection quantity of approximately 2.2 mg/stroke was previously measured via the diagnostic interface (climate control off, no lights on, engine at operating temperature). With readings above 6 mg/stroke, the shaking completely disappeared. With readings above 3 mg/stroke, a significant improvement was still noticeable. While I couldn't provoke any stuttering at the higher values, the power delivery was noticeably more sluggish. Therefore, I've now adjusted it to 3.2 mg/pin. With the air conditioning turned off, only slight fluctuations in idle speed are noticeable when coasting. Result: Ulf's tip is also applicable even with the AHF's unstable idle.

My idle injection volume is significantly above 5 mg/hour. Consequently, my pump should theoretically be set extremely lean, or? Nevertheless, the engine still stutters in the specified speed and load range.
However, there is absolutely no problem when the outdoor temperature is warm during the summer.

Can anyone make sense of it?
Could my fuel injector possibly be sticking at very low injection volumes, with the sluggishness only occurring at low fuel temperatures?

Thank you for your help!

Regards,
Alex.

donalexo wrote:

My idle injection amount is significantly above 5 mg/H. Therefore, my pump should actually be set extremely lean, or? Nevertheless, the engine still stutters in the aforementioned speed and load range. However, when the outdoor temperature is warm in the summer, there is absolutely no problem.

Hi Alex,

Unfortunately, I can't explain it , but I can confirm that mine also tends to jerk more (rarely), the colder it is outside, especially during the warm-up phase.

However, even this less frequent type of stuttering "responds" to the MSW setting or the corresponding adaptation, as described in the technical article.

Did you determine the 5 mg value with a warm engine, without any other load (e.g., lights, air conditioning, charging current for a weak battery)?

@ulf:

Quote:

Did you determine your 5 mg value with the engine warm, without any other load (lighting, climate control, charging current for a weak battery, etc.)?

Unfortunately, it wasn't quite right. While all the consumers were turned off, the engine was not yet fully warmed up. The estimated coolant temperature was approximately 40°C. However, I don't think that has a significant impact, or does it?

For safety, I can take another measurement while the machine is still warm.

Regards,
Alex.

donalexo wrote:

For safety, I can take another measurement while the machine is still warm.

Hi Alex,

I would definitely do that, because it would certainly eliminate one source of uncertainty.

Sure, here's the translation:

'small hint:'

'At idle, the displayed fuel injection amount is incorrect.'

The idle speed control system has the final say; it adjusts the engine speed to 900 RPM.
What is then displayed is the amount attributed to the actuator deflection (adjustable in adaptation channel 1). As long as these values do not reach the limit excessively, the idle speed control takes precedence.
You can clearly see this when you change channel 1. The displayed injection amount changes drastically, and the voltage of the RWG remains at zero millivolts.

It would be best to try adjusting the quantities generally via channel 1. It's possible that wear and tear, etc., could cause the amount to become too low when the machine is cold or the intake air is insufficient.

CU Gremlin.

Gremlin wrote:

When idling, the displayed fuel injection amount is incorrect.... The idle speed control system has the final say; it adjusts the engine speed to 900 RPM. What is then displayed is the amount attributed to the actuator deflection (adjustable in adaptation channel 1). As long as these values do not reach the limit excessively, the idle speed control has the upper hand. You can see this very clearly when you change channel 1. The displayed injection amount changes drastically, and the voltage of the RWG is not even a millivolt...

Hi Ralf,

That's exactly what the "VAGCOM trick" in the technical article about the DIY solution for jerky driving is based on .
Of course, the mg reading depends on the pump setting or adaptation.

High mg values can also be caused by increased power demands of the engine (e.g., cold engine block, air conditioning on, high alternator load), while in the unloaded warm idle state, the mg reading can still be suspiciously low.

High mg values can also be caused by increased power demands of the engine (e.g., cold engine block, air conditioning on, high alternator load), while in the unloaded warm idle state, the mg reading can still be suspiciously low.

That's obvious...

I just wanted to point out that an MG value at idle, by itself, doesn't have an absolute meaning.
You can't just say 'set it to 3mg and that's it.'

It would be interesting to know the voltage of the reverse water pump (RWG) for the different engines, for example, when they are running warm without any consumers connected. Since we all have the same pumps (except for me) and many of us have the same engine type (MKB).

CU Gremlin.

Hello everyone!

I logged the fuel injection amount again today while the engine was warm.
It was approximately 3.8 to 4.1 mg/H.
There's still a significant difference, meaning that friction losses decrease considerably with increasing temperature.

That probably means my pump setting is right in the middle, so it's neither particularly lean nor overly rich.

Regards,
Alex.

donalexo wrote:

Therefore, my pump setting is probably right in the middle, so it's neither particularly lean nor overly rich.

...and with that, no "inevitable" stuttering would be expected.
It might actually be related to the mileage.

You might be able to reduce the jerking by "de-greening" it. It's relatively easy to check this with VAGCOM by performing a downward adaptation of channel 1.