Idle speed in the partially heated area fluctuates.

Hello!

Recently, I have been observing fluctuations in the idle RPM of my TDI ACV. This only happens when the engine is at a specific, somewhat warm temperature. Even a brief increase in throttle does not lower the RPM. Therefore, this phenomenon only occurs at a very specific temperature. What could be the cause? There must be some value that doesn't fit, or could this be related to the disconnected AGR valve??? Since my VAG adapter is a piece of junk, I can't read anything out either,

Greetings,

Peter

Mc_Givertechnik wrote:

Recently, I have observed fluctuations in the idle speed of my TDI ACV engine. This only happens when the engine is at a specific, somewhat warm temperature. Even briefly pressing the accelerator pedal does not lower the idle speed. Therefore, this phenomenon only occurs at a very specific temperature. What could it be?

Hi Peter

Engine temperature sensors sometimes exhibit very strange behavior, according to experiences shared in relevant forums, by providing incorrect values only within specific temperature ranges.
An increased idle speed is usually adjusted when the engine (appears to be) very cold.
Or if the accelerator pedal sensor is detected as faulty... does the car react strangely or not at all to the gas?

Hello Peter,

...Even a brief acceleration does not lower the RPM...

I'm guessing you mean that the engine speed also remains at a high value even after you take your foot off the accelerator

This strongly suggests - as Ulf has already said - that the temperature sensor is the likely culprit. Does your car also run hotter for longer when it's in this condition?
The control unit, however, assumes that the temperature is cold if a faulty sensor is detected. It also preheats (which only occurs at temperatures below 10..5°C), and increases the idle speed.
There is a possibility that the source has a disconnection or short circuit against ground at certain temperatures.

Best regards, Rudi

[Translating...]

Hallo Rudi, hallo Ulf!

Der Temperaturgeber? Ich hatte sowas vermutet. Sonst läuft die Kiste recht fein, keine Auffälligkeiten.

Über welchen Fühler holt sich das Steuergerät denn diesen Wert? Ist es nur der Wassertemperaturfühler im Kühler oder wo anders. Die Temperaturangabe am Climatronic Display gibt richtige Werte aus, also an diesem Lufttemperaturfühler kanns nicht liegen, sollte es von dort kommen.

Danke, Peter

[Translating...]

Mc_Givertechnik wrote:

Über welchen Fühler holt sich das Steuergerät denn diesen Wert? Ist es nur der Wassertemperaturfühler im Kühler oder wo anders.

Hi Peter

der wichtigste Wert kommt vom Kühlwassergeber.

Die anderen dienen in diesem Zusammenhang AFAIK nur dazu, eine (programmierte) Defektvermutung zu begründen --> abgezogener Wassergeber bei heißer Pumpe macht den Warmstart auch nicht (immer) besser.