AFB Symptoms: What You Need to Know

I observed the following in my own car and in a customer's car that was in the workshop today. Both were A6 models with a 2.5 V6 TDI engine. Mine is from 1998 with 190,000 km, while the customer's car has 90,000 km. I need to find the exact year and engine code tomorrow. I noticed that mine is much louder and has a strong knocking sound when cold, which the customer's car doesn't. The customer's car just hums, but mine starts to knock when I touch the accelerator. Also, my car starts immediately when cold, usually with just one engine turn, but when it's warm, it cranks for a longer time, about 3-4 turns. Why is that? It should be the other way around. I have it deregistered at the moment because I plan to do some work on it. Could it be related to the fuel injectors with this mileage? The fuel consumption is excellent, around 7-7.5 liters per 100 km. Are the V6 engines with roller rocker arms perhaps generally quieter? I think the car in the workshop might be one of those.
"And what I've noticed with my variable valve timing (VVT) system is this: when I disconnect the vacuum hose from the VVT solenoid while the engine is running, the adjustment rod drops down, just like it's supposed to. But when I reconnect the hose, it takes about 3-4 seconds for the rod to reach its uppermost position. Also, it doesn't quite reach the upper limit; it stops about half a centimeter short. If I push it up with a screwdriver, it goes all the way to the top. Is this normal? Shouldn't it be reaching the upper limit on its own? That's why there's a stop screw there, but it's not working. I'm hoping you have some tips on what I should do now, since the car is currently deregistered. I want to enjoy the car for a while longer."

Hello, you could put a little more effort into your writing and be a bit more polite.
"The older V6 engines, like yours and mine, tend to be noisier at idle than the newer ones with roller rocker arms. However, if yours is excessively noisy, check the camshafts; they might be worn, which can cause that kind of noise. Regarding the VTG (Variable Turbine Geometry), what you're describing isn't normal. That component should reach its end stop within the specified time, without any assistance. Either your VTG is sticking (in which case you need to move it forcefully through its range of motion and extend the gears all the way), or you have a leak in the vacuum system (a suggestion: check the area in the wheel well where the 'accumulator' is located)."

I hope you don't work in a VAG factory workshop.

No offense.

Greetings from Luxembourg.

The manufacturing year of the other A6 is very important. The VTG (Variable Torque Geometry) system is not working correctly in your car; please check the vacuum pressure in the system.

"What do you mean by 'putting in more effort'? I haven't experienced these symptoms with a V6 TDI engine before, which is why I described it that way."
Is it possible to dismantle and make the VTG (variable turbine geometry) more common? Maybe by greasing something or similar? I haven't had to do anything with a VTG before, except for completely replacing the pressure sensor. I definitely won't be driving it on the road because it's deregistered, and I need to figure out why it's making that noise. I checked again today, and the clicking seems to disappear when it gets warm. Could it be the hydro? What do you think? But it's definitely running lean, it's making a lot of knocking noise when I accelerate. If I slowly increase the engine speed, it barely knocks, but if I floor it in neutral and let it rev up quickly, it knocks very loudly. Given my mileage, do you think the injectors might not be producing a proper spray pattern? What do you think?
So, the other car had a BDG engine and was from the 2004 model year.

Hello everyone,

@Rico Avant: I am certain that your vehicle produces a noticeably louder combustion noise compared to the customer vehicle you described.
The primary reason in this case is the introduction of direct injection, which your engine doesn't have, but the BDG does.

As far as I can recall, Pilot Injection (PI) was first introduced in the 2.5-liter V6 engine with the launch of the 132 kW version. However, it is only used during the warm-up phase; specifically, when the coolant temperature exceeds approximately 75°C, the PI is deactivated.

The derivatives with warm PI (meaning pre-injection even at coolant temperatures above 75°C) were introduced with the B6 model series and the C5PA, but initially were still designated as EU3.

With the switch to D4 or EU4, there was then a change to RSH, an AGR cooler, an electric ALD (Abgasrückführungssystem), a modified injector, and ESP (Electronic Stability Program).
All D4 and EU4 engines also have the "Warm PI" feature, and your neighbors may be able to utilize it as well.
guaranteed to confirm!

Greetings, J.

If the Nagelkiste is an older model, that statement is accurate. To make a comparison, you would need to listen to a comparable model. There is already enough information about VTG in specialized articles.

Okay, I understand now. That was quite an accurate statement.
I'll check the nozzles, and then we'll see.