TDI PD: Loud Intake Noise - AVF Engine

Hello,

'For a few weeks, I've been experiencing various problems with my AVF 130PS TDI PD, manufactured in December 2000, with 71,000 km on the clock. It started with a metallic rattling sound coming from the rear silencer (heat shields) during cold starts, which disappeared when the engine was warm. A few days later, I noticed more or less strong vibrations, especially between 1200 and 2000 rpm. Now, there's a noise coming from the air filter box during acceleration (similar to an open air filter box), accompanied by strong vibrations throughout the vehicle. Additionally, there's a slightly jerky acceleration at lower RPM (likely the mass airflow sensor). Here's what I've already checked:'

Engine mount, transmission mount: No cracks or other abnormalities (inspected before the sound originating from the LFK became noticeable).

CAT: No abnormalities detected during palpation.

Air filter and housing are in good condition.

Turbocharger hoses: No cracks or other damage were found.

Error memory is empty, no entries found.

I'm a bit puzzled, as I'm experiencing a very low-frequency rumbling even when the engine is idling. My mass airflow sensor (MAF) is likely faulty, but I can't imagine that it could cause such symptoms. Unfortunately, I don't have the means to check the boost pressure. If there's a problem with the boost pressure, shouldn't it be stored in the error memory?

I am grateful for any advice you can offer!

Do you have an original paper air filter installed, or parts from an aftermarket supplier?

It is an original VW air filter.

Hello!

The thing about the humming sounds very familiar to me .
Take a look at the air intake manifold adapter, located at the top of the air filter housing.
It is definitely loose (you can easily lift it a little).
You wouldn't believe the noise this thing can make at certain speeds .
They've already installed two completely new intake manifolds for me under warranty. Each time, after a few thousand kilometers, the angled piece would become loose again, making a terrible racket that was unbearable.

Finally, the expert had the simple idea of using a small rubber wedge to fix the angle.
I think the problem could also be solved with a Velcro strap.

Greetings.

I took a closer look at the intake manifold (which is attached to the front crossmember). Unfortunately, it's quite tightly fitted at the transition to the air filter box . I will still try to fix it additionally, maybe it will help .

How about the jerking/stuttering? Is it only within a certain RPM range, or is it a constant stuttering that depends on certain load conditions?

It's a wave-like acceleration between 1200 - 2200 RPM, which I've noticed, but it only happens when I accelerate out of curves while driving in city traffic. In addition to the extreme rumbling and vibration, there's now also a hissing sound (which might indicate a faulty turbocharger hose, but I can't find any cracks or damaged hoses). I've lost count of how many times I've had it on the lift.

hmmmmm...

The jerking could also possibly be caused by the EGR valve. Try to somehow seal it.

Otherwise, it will be difficult without a VAG-COM diagnostic tool. Do you perhaps have a way to borrow one, so we could check things like boost pressure? Also, given the age of your car, it's possible that the O-rings on the pressure control elements (PDEs) might be defective.

Unfortunately, I don't know anyone with a VAG-COM diagnostic tool. I only have a Gutmann (I think it's a Gutmann) diagnostic tester available. However, even this should detect over-boost pressure in the turbocharger if it's stored in the error memory... or should it? At least, it detected overpressure in the turbocharger on a Golf 4 1.9 TDI. However, according to the tester, my error memory is empty.

Don't focus solely on overpressure; underpressure isn't always considered an error.

Okay, close the AGR (exhaust gas recirculation) and then we'll see if the engine still vibrates. Okay?

Okay, I've found the AGR valve, I'm going to disable it now and test. I've also noticed something else: when I'm going downhill and I disengage the clutch and let the car roll, the engine speed fluctuates between 900 and 940 RPM. It's not critical, but it's not normal either.

AGR system deactivated, no more jerking during acceleration so far. The noise is still present. Is it normal to have an oil film in the hose between the air filter and the turbocharger?

'Oil film is normal as long as it's not leaking excessively. I also know that rumbling sound from mine. It's been there since day one, I think... Just observe it for now. If it gets worse, we'll need to investigate further. But at least the jerking is gone. That's something... (or rather, the most important thing).'

First of all, thank you! Also, the fluctuation in speed while driving downhill has now disappeared. However, the droning is very annoying. In addition, I drove a different 130PS TDI PD Passat this weekend. It's a difference like night and day. It pulls better and is much quieter than mine. Now I've realized how much my car idles roughly! I suspect a misadjusted injection timing (thanks to this site, I'll probably become an expert ). Maybe that's also why I have such strong vibrations. I've now ordered the diagnostic adapter kit KKL (RS232) with VAG-COM. Well, it doesn't really matter. Also, you can probably adjust the injection timing with it.