Passat 1.9 TDI AVF: Vibrations, Jerking & High Fuel Consumption

Hello everyone.
I've owned a Passat with an AVF TDI engine, manufactured in 2002, for the past 2 months. It has 247,900 kilometers on the odometer.
I'm generally very fond of this vehicle, but it comes with a whole range of problems.

The following problem:

Problem 1: Rumbling/Vibration.
As soon as the engine starts, there's a vibration inside the cabin. The noise level increases with the engine speed, creating a booming sound inside. It's more pronounced after a cold start than when the engine is warm. It feels stronger on the driver's side compared to the passenger seat. There's also a buzzing sound that can be heard, especially when the engine is cold, starting around 1600 RPM.
Both engine mounts are new, and pressing the clutch pedal doesn't help; the vibration persists. The Bosch service says it's the dual-mass flywheel. However, the clutch is disengaging properly.

Problem 2: Jerking or stuttering when using cruise control.
The Bosch technician says: if the injectors or the wiring harness (which was checked and deemed to be in good condition by the Bosch service) are faulty, the car will jerk during acceleration. Mine runs smoothly, except when I use the cruise control at, for example, 120 km/h.
Occasionally, there's a slight jerking sensation. Sometimes it's more noticeable, sometimes not at all, but it feels like it's only happening when the cruise control is engaged.

Problem 3: Consumption.
In short, I need to make an effort to get 800 kilometers on a single tank of fuel. The display shows a consumption of 7-8.5 liters.

Replacement parts installed in the last 1000 km: timing belt kit including water pump, alternator, both engine mounts.

I have a skilled friend who is a trained automotive technician and has a diagnostic tester. However, he rarely has time.

I'm from the Aachen area and would also be willing to bring the car within a 250km radius for diagnosis/repair. Unfortunately, my regular mechanic has passed away, and currently I'm just going from one conspiracy theorist to another.

Best regards, Mario.

What is the measured fuel consumption? Record the kilometers driven after a full tank, drive, fill up again, and calculate. Which method is the best over several thousand kilometers?

Forget about gadgets like on-board computers.

"7-8 liters per 100km is perfectly normal for a 3BG TDI, as long as you're not driving like you're trying to set a land speed record and you're not driving barefoot."

A worn-out ZMS (Zentrale Massenscheibe) usually has absolutely nothing to do with the performance of the clutch.

Has the serpentine belt ever been removed to check if a driven component has a bearing failure? It's a quick check to do.

"The flexible pipe is intact, but even that can cause unpleasant noises, just like a loose ceramic element in the catalytic converter."

Quote:

Problem 1: Rumbling/Vibration. As soon as the engine starts, there's a vibration inside the car. Along with the engine speed, a booming sound enters the cabin. It's more pronounced after a cold start than when the engine is warm. It feels stronger on the driver's side compared to the passenger seat. There's also a buzzing sound, especially when the engine is cold, starting around 1600 RPM. Both engine mounts are new, and pressing the clutch pedal doesn't help; the vibration persists. The Bosch service says it's the dual-mass flywheel. However, the clutch is disengaging properly.

Rüdi has already written to you about the knocking sound. However, it can also have other causes, such as uneven compression, a worn camshaft, etc.

To avoid having to rely on guesswork or speculation, you would need VCDS!

Quote:

Problem 2: Jerking or stuttering when using cruise control. The Bosch technician says: if the injectors or the wiring harness (which was checked and deemed to be in good condition by the Bosch service) are faulty, the car will jerk during acceleration. Mine runs smoothly, except when I use the cruise control at, for example, 120 km/h. When you turn it on, you occasionally feel a jolt. Sometimes it's more, sometimes it's none at all. But it feels like it only happens with the cruise control.

Öm, I also had something similar with my 3B once... The speedometer sensor (on the transmission) was defective, and it was probably causing very short interruptions... which confused the cruise control .

In addition to Rüdi's answer, a note about the alternator's free-running mode. If this is defective, the tensioner for the serpentine belt will make a very loud whining noise and vibrate significantly. This noise should disappear when the belt is removed.

...and the generator's free-running function can be quickly checked with the belt removed.

The PD cable harness cannot be properly inspected, so it's best to replace it to be on the safe side.