Idle Speed Drops When Braking

Hello,

Recently, I've noticed that when braking (e.g., on a country road at a traffic light), the idle speed drops by about 100 RPM (visible on the tachometer). After a short moment when the car is stopped, you can observe how the RPM returns to the normal idle level.

I'm surprised that this increase doesn't happen continuously, i.e., during the braking process.

I mainly notice this when performing longer braking maneuvers, as I mentioned, like when slowing down from 80 km/h on a country road. Of course, I'm not applying full braking force (to preempt any doubts).

Have you made similar observations?

I assume that the BKV (likely referring to a component related to engine management) increases power and, consequently, puts more strain on the vacuum pump. I also have an additional problem with my ATJ engine: When I disengage the clutch or shift out of gear at approximately 1,000 RPM, the idle speed drops to as low as 777 RPM (according to VAG-Com). However, I will have the idle speed adjusted to a higher value (I don't have a licensed version of VAG-Com myself), as it is currently at the lower end of the target range (approximately 800-820 RPM when warm).

Best regards, WarLord.

"This is normal and not a bad thing (although 100 RPM is quite a lot...). Try turning on the air conditioning or another large electrical consumer while the engine is idling. This will cause the idle speed to drop momentarily, and when the control system detects this, it will immediately increase the diesel injection (you'll see the instantaneous fuel consumption on the MFA display increase!). That's perfectly understandable. The idle speed will only be adjusted back to the target value once a certain threshold is reached."

Hi,

"Mine does the same thing when I suddenly release the accelerator and apply the brakes at the same time. How hard I brake doesn't matter; it's all about the timing of the pedal movements."
I suspect there's more likely a bug in the engine control unit software...
Nothing serious.

Best regards, Rainer.