BDG - unstable idle during warm-up phase

Hello,

'For some time now, I've been experiencing a problem with my BMW (mileage approximately 86,000 km) where the engine runs roughly at idle before it reaches operating temperature. Once the engine is warm and during normal driving, everything seems fine; there's no noticeable loss of power, at least not any different from before.'
The uneven idle speed doesn't just occur after a long period of inactivity, but whenever the engine cools down slightly.

When I had a similar problem last summer, but only when the engine was warm, the engine control unit (ECU) was replaced, and the problem was resolved.

The following items were inspected or replaced by the workshop:

- The idle air control system showed values up to 2.5 mg/h on one cylinder. A nozzle (needle valve) was then replaced, and the values for the idle air control system returned to normal.

- alle Düsen abdrücken lassen - Spritzbild u. ÖOpening pressure OK.

- Compression test OK.

- Camshafts are okay.

- Replaced a motor mount (due to a faulty memory entry).

- Current status of MSG software.

The workshop foreman is at a loss; Audi recommended replacing all the injectors, but the workshop rejects this suggestion because they appeared to be fine after being tested. The foreman will be attending training this week and plans to discuss the issue with experts there, but I'm asking for ideas here about where the problem might lie.

I'll investigate further regarding air in the fuel system (but why only when cold?), and also check the plausibility of the values from the temperature sensors. I won't have my VAGcom diagnostic tool until the weekend. It's a bit vague, but those are the things that come to mind.

Sure, here's the translation:

'Thank you in advance.'

Greetings.
Jean.

It will be difficult to diagnose the problem without measuring it during the relevant operating phase. Perhaps the automatic fuel-injector return (AGR) system is malfunctioning, or the hydraulic lifters may need to be filled with oil. Tapping noises are not always easy to detect in a diesel engine.

Hello,

I'm bringing this topic up again because the problem still persists.

The mileage is now 130,000 km.
Meanwhile, all the fuel injectors have been replaced, and the engine now runs a bit smoother.
AGR works.
At an engine temperature of approximately 70°C, the value in the idle speed control system for cylinder 1 is between 1.63 and 1.80 mg per cycle. When the engine is at operating temperature, this value decreases to 0.70 mg per cycle, while all other cylinders are within the range of 0.1 to 0.26 mg per cycle.


Is there any idea about this?