Engine Brake Issues & Increased Fuel Consumption

Our 1.9 SDI Fabia has 105,000 km on the odometer. Recently, the engine braking effect has deteriorated significantly. It almost rolls freely without any braking. I have the feeling that it's injecting the amount of fuel needed for idle while rolling, which makes it roll much more easily (or the compression is significantly reduced - hopefully not).
'This surge caused by the re-injection when reaching the idle speed range while rolling is no longer present. The fuel consumption has also increased by up to 1.5 liters. Otherwise, it drives normally. Another thing I've noticed is that before, there was always a slight 'shaking' when the engine was turned off, but now it shuts down much more smoothly.'
What could be wrong, and where is the 'torque reduction control' actuator located (in the ESP system)?
The error memory doesn't show any errors, but the ESP is leaking slightly (likely due to biodiesel damage). Bosch will check it soon and, if possible, re-seal it; otherwise, it will be replaced. Perhaps the problem lies there, or maybe there's something wrong with the EGR valve.
I would be very grateful for any information, as I have the impression that the Skoda workshop is trying to overcharge me for an AT-ESP (1000€).

Hello OJ!

Does the idle speed control work properly, or does the engine sometimes tend to "stutter" at idle? Do you experience any other jerking or hesitation problems at low engine loads?

To me, this sounds like a stuck throttle valve that is unable to reduce to the zero quantity setting. If the idle control is still working reliably, then the "set point" must be somewhere between the idle injection quantity and the zero quantity.

You might want to run some diagnostics using VAG-COM. It would be interesting to see the logs of the fuel injection quantities (actual injection amount) and the logs of the RWG voltage. The voltage interval of the RWG might also be interesting for evaluation.

Regards,
Alex.

'The idle speed is normal and consistent, I would say. Unfortunately, I can't read any data with VAG-Com yet (I still need to build the adapter cable). Why didn't the workshop perform additional tests when I explained the symptoms to them (I wasn't present at the time!)? They just said it's 'biodiesel damage because the ESP is leaking'! They probably really want to install a new AT-ESP at an expensive price. I need to see what Bosch says first. Does anyone happen to know the exact model number of the ESP from the 1.9 SDI Fabia? It's not much fun to look at it in the cold and late after work. The Bosch service needs the model number to order the seals. Thanks in advance!'