Rattling noise at idle

Hello,

I haven't been driving a diesel car for very long, so I don't necessarily have the knowledge to answer my following question. I've also tried searching online, but I couldn't find a satisfactory answer to my problem.

I drive a Volkswagen Golf 3 TDI with the engine code 1Z, manufactured in 1996, and it has approximately 170,000 kilometers on the odometer.
In the engine speed range of approximately 1500 to 2600 RPM, I hear a rattling sound coming from the engine compartment. It's a kind of light, metallic rattle, like when you place a small nut on a vibrating metal sheet.

I hear the noise inside the car, and I think it's coming from the front, specifically from the engine compartment. If I roll down the window, I don't hear the noise from outside. However, I can clearly hear the turbo whistle.

Furthermore, I've noticed that when accelerating from 50 in third gear to just below 3000 RPM and then shifting into fourth gear, the noise isn't present, because the engine speed after shifting is around 2200-2400 RPM. It only happens when trying to accelerate out of the low RPM range.
It's possible that I'm imagining it, but it seems loudest on the third floor.

Driving in the fifth gear at 50 km/h is not possible because the engine jerks slightly; the RPM then drops to 1000. It is possible to drive at 60 km/h in the fifth gear, with an RPM of 1100.
It's surprising to me too, because I've often read here that some people drive at 50 km/h in the fifth gear.

I can't really tell if the vehicle has a power loss because I haven't had it for very long. However, it definitely pulls smoothly between 2000 and 4000 RPM without any hesitation, and it easily reaches 180 km/h on the speedometer. I wasn't able to test whether it could go faster due to traffic conditions.

Where is this noise coming from, or how can I locate it?
Or what could it be?

Thank you for your help.

"I also have the feeling that the car has a slight tendency to stall when starting, and I don't notice a significant turbo lag, at least not as much as in the company's TDI (PD) with 100 hp."

Hi,

You might want to read this post about your problem.

/viewtopic.php?t=2149&highlight=ribbon belt tensioner

The 1Z engine has a turbocharger with a wastegate that provides very little boost in the lower RPM range.
The company car (either with an ATD or AXR engine, both 100hp PD TDIs) has a VTG turbocharger, which significantly shifts the turbocharger's response to lower RPM ranges.
Furthermore, the 1Z engine currently produces 202 Nm of torque, while the ATD/AXR engines produce 240 Nm – you should definitely notice the difference. So, if the 1Z engine can easily reach 180 km/h, then it shouldn't be lacking in power. You could try performing the "Ulf's acceleration test" for a comparison.

/viewtopic.php?t=3142&highlight=throughput test
/viewtopic.php?t=209&highlight=throughput test

Hi,

A faint rattling sound can sometimes originate from a loose heat shield, even in the simplest of cases.
I experienced this issue repeatedly over a period of 7 years with my 1Z car.
Depending on the load and speed, the vibration can cause a rattling noise.

It's my opinion that the jerking at 50 km/h in 5th gear isn't a major issue. This happens with many single-cylinder engines. Depending on the fuel injection pump settings, it may occur more frequently or not at all.

Hello,

Since your problem seems to occur more often at low engine speed and high engine load...
I'm looking for the error in the exhaust system area.
Have you ever looked under the car to see if there are any brackets or supports missing?
Should the exhaust system, starting with the front pipe and including the catalytic converter, be attached to the body?
Does the rattling change with engine speed?

I'm going to check the insulation panel later tonight.
I highly doubt it's the exhaust; I had a similar issue with my old car before, but it sounded different there. The rattling sound I'm referring to is more likely located in the higher frequencies.
I'm not sure if the rattling actually stops at 2600 RPM, or if I just can't hear it anymore because of the engine noise; the engine gets quite rough at that speed.
The sound is changing; the noise seems to be getting higher in pitch because it's apparently being "rattled" faster and faster until I can no longer hear it.
Hmm, it's a bit difficult to describe, so I apologize for the wording.
But checking things like the exhaust gaskets isn't really a problem.

I've actually performed a permeability test before, at approximately 25°C.
It took 8.29 seconds to reach that speed (2,000-4,000 RPM) in third gear.

The issue might be with the tensioner pulley; it's only had its second timing belt, so it might need to be replaced again now.

The noise is quite annoying; "ringing" might be a way to describe it.

Hi,

If it sounds more like a ringing or rattling noise, I would agree with Bertil – or rather, the first link he provided.
Spanners are a real problem with the 1Z.
Within the first 50,000 km, I needed to replace two of them.

Hello!

I once had a similar rattling noise. As Markus H. reported, it was a heat shield that had come loose from its bracket.
It could also be a defect in the flexible part of the exhaust system, just behind the manifold. Supposedly, this is a common weak point on TDI engines, although I haven't read about it before, nor have I experienced anything like it on my 1Z so far.

Best regards, D.

Okay, I'll take a look at it tomorrow. Luckily, I have vacation tomorrow.
So, on my way home today, I tried again to identify the noise. It's kind of like the rattling sound you get when you shake a large set of keys in your hand.

This vulnerability is called FLEXROHR.

If that's the case and the piece is connected to the flexible pipe (as it was in my situation), then you're completely screwed.

Then you are allowed to put €600 worth of parts on the table!

Let the car idle and get underneath it. If the rattling stops when you hold the catalytic converter, then it's either the catalytic converter itself or the flexible pipe.

The flexible pipe is a weak point in the 1Z because the entire exhaust system, from the turbocharger to the middle muffler (located under the rear seat), hangs freely (almost 150 cm) and moves around quite a bit.



They noticed the issue with the AFN and AHU and reattached the pipe in front of the catalytic converter.
In addition, they have a longer and therefore more flexible bellows.


Okay, please provide the German text you would like me to translate into English. I will only provide the translation.

Okay, I tried to locate the noise while the car was stationary. No luck. When I floor the accelerator pedal with the engine idling and let it reach that specific RPM range, nothing happens. It just sounds like a diesel engine.

That doesn't exactly make the diagnosis easy for me; it seems that the problem is probably not related to a faulty component, but rather caused by something hitting or impacting something else.

I then checked all the hoses and brackets in the engine compartment, and also repositioned the outer casings of two hoses that run towards the interior of the car. These were flexible metal tubes.

Then I drove it, and lo and behold, the noise is much quieter and stops just above 2000 RPM. I'll keep monitoring it; I think I've found the culprit.

I also found a loose piece of "damping material" that's about 6 cm long. It's basically a tube made of foam, probably 6 cm long and at least as thick, with one side cut open and a small hole in the middle, so you can slide it onto a small tube.
It might be related to that somehow. I just don't know where it belongs.