Diesel Flush & Relay 109: Repair & Replacement

'My Passat 1Z, manufactured in '94, occasionally exhibits a relatively mild, regular 'shaking' or 'vibration' under partial load conditions (up to approximately 2500 RPM). This shaking disappears when I accelerate.'
This shaking isn't just an illusion; it's particularly annoying, especially on country roads or highways (around 85 and 105 km/h), when you're trying to maintain a constant speed.
Occasionally, I also notice a slight, unusual fluctuation in the idle speed, by a few RPM.

I've already tested the knock sensor with the 'knock test,' but it seems to be working fine.

I've read online a few times that cleaning the fuel injection system can be helpful, so I wanted to ask if anyone has had any experience with that.
I imagine it like this: You buy a diesel cleaner, for example, from Liqui-Moly, but instead of putting it in the tank, you disconnect the hoses from the diesel filter and let the engine draw the cleaner directly into the system using the starter.
Once you've done that, it's likely to be beneficial to let the fuel system soak with the cleaner for a few hours before reconnecting the normal fuel lines to the filter.

What do you think about this????


Could such jerking also be caused by the much-discussed relay 109?
Can this be checked in any way, since my error memory is empty?
(Is a faulty relay displayed there?)


The engine otherwise runs very well, meaning it delivers its power (90 horsepower ).
The shaking/jerking is independent of the temperature!

Thank you, Best regards, BASTI!

Hi Basti,

Diesel fuel additives can be beneficial, but the ultimate recipe for optimal results (at least here) probably doesn't exist.

Relay 109 can cause "hard" jolting, although this is often accompanied by nonsensical error messages.

"Soft" jolting or jerking seems to often originate from the mass airflow sensor (MAF sensor) --> clean or replace it.

I've already cleaned the LMM, and it wasn't particularly dirty; it actually looked quite good!

Are you saying I should have the flush and the relay replaced?!?!?

Best regards, Basti!

Basti911 wrote:

I have already cleaned the LMM, and it wasn't particularly dirty, and it actually looked good! You mean, should I have the flush and the relay replaced?!

Hi Basti,

if the mass airflow sensor (MAF sensor) is broken (which I think is possible in this case), then cleaning it will not help anymore .
But trying with 109 or a cleaner would be a cheaper option before considering a replacement.

If I were in your place, I would first open the 109 and look for cold solder joints or clean the switching contacts. Then, the relay would almost certainly be working again without having to buy a new one }.

What does 'cold solder joint' mean?
Is it even possible to open the relay without damaging the housing?

I don't think the LMM is faulty, because the fuel consumption and performance are perfectly normal.

Basti911 wrote:

What does "cold solder joint" mean? Can the relay be opened at all without destroying the housing?

Hi Basti,

A loose connection in a soldered joint. This can happen during manufacturing or if something becomes loose in the solder due to constant vibrations.
My relay can be opened by inserting one or two screwdrivers into the edge of the bottom and prying it open.

Quote:

I don't think the mass airflow sensor (MAF) is defective, because the fuel consumption and performance are perfectly normal.

However, it might have a minor issue that causes fluctuating acceleration, which can sometimes be resolved by replacing the mass airflow sensor (MAF). I don't understand why, but there are always reports like this circulating.

Just for your information:

A new relay 109 costs less than 12 euros from the 'friendly' dealer.

Best regards, D.

I've opened the relay now.
It actually looked brand new on the inside: the coil was clean, and the solder joints were solid.

I think I'm going to do a rinse now.

Is it okay to directly suck up the 'dish soap' and let it sit in there for a while? What happens if you start the engine again afterwards, since the stuff will be concentrated in there?


BASTI!

Basti911 wrote:

Does it matter if you suck the "dish soap" directly into the engine and let it sit for a while? What happens if you start the engine again afterwards, since the stuff will be concentrated inside?

No problem, I've done it that way before. The Reniger serves as a diesel replacement.

Did it make a difference?
What cleaner did you use?