Air Flow Meter Test: Old Style with Slide

Hi.
Since I'm still trying to find the remaining 'residual vibration' despite having replaced the pump, I consulted the helpful book 'Now I'll do it myself' and checked the values of the individual temperature sensors (values within normal range), the coolant temperature sensor (91 ohms, within normal range), and also the mass airflow sensor (MAF). According to my description, the MAF sensor should provide a voltage of 0.5 - 1.5 V between contacts 2 and 4 when idling. The supply voltage of 4.5 V is okay. However, the measured voltage at idle is 2.03 V.
Unfortunately, I wasn't able to take measurements across the entire RPM range because I was working alone.
Does this voltage reading already suggest a faulty mass airflow sensor, or is the information in the service manual incorrect?
Unfortunately, the AGR (Automatic Gearbox) has failed. It should be closed in neutral, though, shouldn't it? If I'm wrong, the increased voltage might also be caused by the increased amount of fresh air being drawn in.
If anyone could perform a measurement on their B4 with the older Mass Air Flow (MAF) sensor version, or confirm the voltage reading of 0.5 - 1.5V, it would bring me much closer to identifying the problem.
Unfortunately, the old LMMs are extremely expensive, costing around 360 EUR .
Maybe someone still has one lying around and would be willing to give it away for money .

Thank you and best regards.
Hermann.

What is the name of your "old LMM"?
So, please provide the part number.

m;

Hi!
Actually, the EGR valve should also be mixing in exhaust gases at idle, so the voltage you measured might be caused by the blockage. However, in modern TDIs, the EGR valve is closed after a short period at idle (about 2 minutes) and only opens again for another 2 minutes after a brief acceleration. I don't know if your car does this, but it's likely to be similar.

Dirk.

@dieselmartin
I'm going to ask my LLM tonight what name it responds to .
I'll write it here. To my knowledge, there should only have been one version available for that year of manufacture (with a fixed window). The hot-film mass airflow sensors weren't introduced until later.

Regards,
Hermann.

@dieselmartin
Okay, here's the part number of my mass airflow sensor:

I called 028 906 301, and he shouted 'here.'

Maybe someone else has one of these?

Regards,
Hermann.

Oops.

That's an air volume meter - does it also fall under the price amnesty for air mass meters?

Maybe your local VW service center can help; they've helped Faxenmacher before.

I'm sorry, but I cannot access external websites or specific files online. Therefore, I am unable to translate the text from the provided URL.


m;

Oops,

That's an air volume meter.
m;

Yes, yes, I wrote that.
'Price amnesty?' At 360 EUR, it's more likely you'll be looking for a used, functional one.

Regards,
Hermann.

Amnesty is being granted because the prices for MASSEN products have been reduced from 180-250 EUR to a general price of 80 EUR (although this includes a trade-in).

Even the old Pierburg units in the 1Z .

m;

Unfortunately, I will hardly be able to participate in that.

Regards,
Hermann.

Hi Hermann,
I have the same one as you, let's see if I can find some time tonight to measure it.
Supposedly, the old parts are supposed to last forever!
Regards,
Sausage blinkers.

Hello Hermann!
You can best measure your air flow meter using an oscilloscope or an analog multimeter (requiring a delicate touch!) during a noise test.
Okay, here's the translation:

'Connect the full battery voltage, 12 volts, to the power terminal, with the negative terminal connected to ground. Then, connect the multimeter with the positive lead to the signal terminal and the negative lead to ground. Slowly depress the throttle valve. If you observe a drop in the signal during this process, then your mass airflow sensor (MAF) is likely defective. If not, then this potential cause of the problem can be ruled out. The measured voltage of approximately 2 volts at idle seems reasonable. Unfortunately, I don't know the exact voltage that should be present at full throttle for your MAF sensor, as it can vary from 5 volts to the full battery voltage. Damage often occurs on the contact surface in the middle range of the valve's travel, which corresponds to the partial load range. I'm not sure in which range your engine is misfiring, but it's possible that your suspicion is correct.'

Best regards,

Dominique.

Thank you, Dominique.

I'll test that. Before that, I'll try another measurement using VAG-Com. The 'drop' should also be detectable then.
By the way, it's operating exactly within the partial load range.
Hopefully, I'll have my interface sorted out by then...

Regards,
Hermann.

Good day.
The airflow meters are powered by 5V, not 12V.
Best regards,
[Your Name/Nickname]

Hi Mucki.

I was aware of the ~5V supply voltage; I had already mentioned that in the first thread. I would have also tested it with a maximum of 5V. Thank you again.

It's still uncertain whether the old version can be replaced with a new one (without the windshield). Perhaps someone here knows something about it.

Regards,
Hermann.

D. Kurz wrote:

You can best measure your air flow meter using an oscilloscope or an analog multimeter (requiring a delicate touch!)...

Hello,
I remember those from the Peugeot 205 GTI as well.

Here's the testing method I used:
Apply the operating voltage and feed the output signal into the input of an audio amplifier (with volume control!) via a small capacitor (approximately 100 nF). Make sure to connect the amplifier's ground to the LMM ground.

Ideally, when manually moving the valve, only a slight, relatively even noise should be audible.
The more popping and crackling sounds you hear, the more worn out the potentiometer is.

With Bosch/Peugeot parts, it was possible to bend the contact spring so that the wiper ran on a new track on the resistance strip (closer to the rotating axis). With a bit of luck, this could sometimes restore trouble-free operation for tens of thousands of kilometers.

Thank you, Ulf.

I'll try using VAG-Com on Thursday.
Let's see if there might be an error there.

It's quite annoying to still experience a slight vibration at 1200-1400 RPM after replacing the pump.

Regards,
Hermann.