TDI Idle Issue: High RPM at 1.4 AMF

Hello everyone,

Here's the translation:

"I'm experiencing the following problem with my AMF engine (manufactured in 2000) which has 100,000 km on it and has not had an EGR system installed for the last 60,000 km."
The machine is actually running perfectly fine.
"For several months, I've been experiencing an intermittent issue where the engine unexpectedly and jerkily revs up to around 2000 RPM, or even less, when starting (as if someone is constantly tapping the accelerator). Then, it automatically drops to almost idle speed (1100-1200 RPM). After completely irregular intervals, the problem disappears, and the idle returns to 800 RPM."
The error almost never occurs during a cold start. However, it happens quite frequently when starting the engine shortly after it has been used. Interestingly, the engine temperature itself does not seem to have any influence.
I had read the error codes before when the problem occurred, but I didn't find anything. Recently, I haven't done that because a friend of mine has been using the diagnostic tool for months, so I need to borrow it again soon (grrrr).
Then I could also log some data, if that helps. But maybe someone already has an idea.

I hadn't really paid much attention to the strange behavior before. I had attributed it to a possibly malfunctioning accelerator pedal.
Unfortunately, this problem is occurring more frequently, and it's not good for the loader to be revved up so quickly after starting. By the way, when it revs up, there's black smoke, not blue smoke from oil. However, a few days ago, the engine suddenly lost 100ml of oil (it doesn't normally consume any).
I no longer believe that the throttle position sensor is related to the problem.

And that is for the following reasons:
The engine speed doesn't normalize even when I slightly adjust the accelerator pedal.

"When I release the clutch, the engine revs up quite a bit without me pressing the accelerator. Then, when I abruptly disengage the clutch, the engine often jumps to around 2000 RPM before dropping back down to its normal idle speed of 1100-1200 RPM. I've found that if I start the car this way frequently, the idle speed tends to normalize more quickly."
Is it possible for there to be any errors in the traction control system?

The sudden increase in oil consumption (which is now back to normal) naturally makes me suspect a problem with the charger.
The car has been chipped for 60,000 km. On the previous car (same model), the turbocharger leaked at 100,000 km (oil leaked through the shaft into the fresh air intake). However, that car had the chip installed since 80,000 km and had problems with overboost from the beginning. Additionally, it was driven frequently on mountain roads in high heat and under heavy load.
However, none of the conditions mentioned apply to my current car.

I haven't disassembled the turbocharger yet, because I'm waiting for the VAG-Com adapter and I don't feel like dealing with it right now. There's definitely oil in there, but the question is how much. However, since the car is performing normally, it probably isn't enough to definitively conclude that there's a turbocharger defect (in my experience, the mass airflow sensor usually throws errors with implausible values first).

So far, so good.
Maybe someone has an idea.
Otherwise, I would also like to know which maintenance workbooks (MWBs) you think I should reasonably consult given the error.

Regards,

Olaf.

Okay, I'll start by reading the error codes. Then you can check the values of the temperature sensors. I don't know which control module (ECU) they're in (do you not have idle speed control?). You can compare the target values with the actual values everywhere, and also check the dynamic fuel injection start.

Without a prior diagnosis, I wouldn't start tinkering. You'll just end up with dirty fingers.

"However, it does have an idle speed control system. But don't get your hopes up about that, because once the engine is properly adjusted, it will stay at a constant 1100 RPM. I will definitely check that once I have the tester, though."

Regards,

Olaf.

dyn. Start of funding?

AMF is a PD.

m;

I hadn't commented yet because I wasn't sure if I might be the one who was wrong...

Hello Olaf!

I suspect a faulty temperature sensor. It could also be a loose connection.
This completely explains the behavior.

Regards,
Alex.

"Thanks, that's probably it."
I had already suspected that the thermostat was faulty, as the vehicle's water temperature would occasionally not exceed 70 degrees Celsius on certain stretches of road, but then would sometimes return to normal.
I hadn't thought about the thermostat, as the car really didn't get warm (you could tell by the heating performance).
In my experience, a faulty temperature sensor would often cause the display to get stuck on a certain reading for a while, before suddenly jumping to the correct position. However, the engine would still warm up properly.
Well, it seems there are apparently different failure patterns.

I had another repair done at the same time, so I have no idea where that part is located.
Is it about the thermostat?
Is there anything else that needs to be removed for the replacement (like the alternator when replacing the thermostat)? I have long and thin fingers.

Thank you for the information, anyway.

Olaf.

Olaf wrote:

I hadn't commented yet because I wasn't sure if I might be the one who was wrong...

For that, but I Once wrote something like this, which is how I started with mine. I just knew that you don't have a 6-cylinder engine...

"If the vehicle isn't reaching its operating temperature, it's likely the thermostat, just like it was for me. However, I didn't experience the exact problems you're having. If the sensors are reporting the correct temperatures, then it shouldn't be causing these symptoms, right? That would mean your vehicle is consistently exhibiting this problem at a specific temperature during the warm-up phase."

I was going to replace the thermostat anyway, but I'll check the temperature readings with VAG-COM to see if they are reasonable (at least I'm sure that even a PD engine has temperature sensors )...

"Neenee, Donalexo is right, it's most likely the temperature sensor. That sounds plausible. Also, I've indeed noticed that the error never occurs when the engine is completely cold."
I've also found the part now. However, I haven't managed to win the battle against the completely stuck connector yet.
It's quite possible that it's just a loose connection (due to the vibrations from the 3-cylinder engine). However, no cables appear to be broken.
Fiddling with the plug definitely won't improve anything.
I suspect the sender unit is probably faulty. So, I'll wait for my friend's tester and, if there's still no change, I'll replace the sender unit.

To my friends:
Can this be done without draining the coolant?
If not, I'll probably invest a few euros and have the workshop do it (I don't feel like messing with coolant in this cold weather).

/viewtopic.php?t=11090&highlight=coolant

Olaf wrote:

In my experience, a faulty temperature sensor

always exhibited the behavior of the display getting stuck at a certain point for a while, and then suddenly jumping to the correct position.

Herr Antje wrote:

Well, Mr. Antje already put it very aptly: At least I'm sure that even a PD temperature sensorhas

some

Olaf wrote:

. Your car also has a dual temperature sensor, one for the engine management system (MSG) and one for the instrument cluster (KI). Your errors indicate a faulty MSG sensor, while the experience you described suggests a faulty KI sensor. However, you should replace both sensors, as they are housed in the same unit (recognizable by the four wires).

However, I haven't yet won the battle against the completely stuck plug.

Olaf wrote:

Bent metal hanger?

Is it possible to do that without draining the cooling water?
It depends on how fast you are .
Seriously: If you release the pressure beforehand and then close the system again (briefly open and close the expansion tank cap), then not too much coolant will leak out during the change. The expansion tank itself is just plugged in, so you can perform the change very quickly (release the clip, remove the old one with one hand, insert the new one with the other hand. Then, simply reattach the clip and plug in the connector. You may also want to check the coolant level and top it up if necessary.)



Regards,
Guste.

EDIT: Dieselmartin was faster (in writing, not in changing }).

Oh, so you have to spell "coolant" with "ue", great.
Thank you anyway.
I just met an ADAC technician outside my door.
He says that if there are no error codes in the system, it could potentially be due to excessive pressure from the fuel pre-pump.
He says I should disconnect the battery first, before I do anything else.
Well, I guess I should probably wait for the test results first and then decide what to do.

Regards,

Olaf.

P.S.
Regarding the metal clip on the plug:
It looked like a normal VW connector with that plastic nose. Did I miss something?

Olaf wrote:

No, Donalexo is right, it's probably the temperature sensor. That sounds plausible. Can this be done without draining the coolant? If not, I'll probably invest a few euros and have the workshop do it (I don't feel like messing with coolant in this cold weather).

I don't understand what you're saying. I wrote in my (1st post) that I used VAG-COM to check the temperature values for plausibility... and in my (2nd post) that a thermostat usually doesn't cause that kind of behavior.

It should be clarified whether it's displaying incorrect readings or whether it's truly not reaching its operating temperature (since there are two sensors, the combination instrument and the engine control unit). If it's not reaching the correct temperature (mine only reached a maximum of 70 degrees), the thermostat should also be replaced. It's less likely that both are broken (they're in the same housing in my case), especially since the combination instrument is displaying something, just not enough. Testing this thermostat is easy for anyone to do.

Regarding my V6:
You can replace it without draining the system, but you need to be quick (some fluid will inevitably spill, as it's contained within the coolant). Replace the seal. Check the fluid level and top it up if necessary.

edit: I guess I was the slowest, there are already 2 extra posts. Well, as long as my help isn't really needed, or I'm portrayed as a novice, I'd better disappear. Oh, by the way, the temperature sensor replacement also went smoothly for me without help, just like the thermostat replacement... I'm not familiar with 3-cylinder engines, but some things are generally applicable, and not all 3-cylinder drivers are experts, right?

Neenee. It is only partially correct .
The issue with the coolant temperature not reaching the proper level only happened once. I was about to replace the thermostat, but then it suddenly started working normally again.
The indicator for the temperature gauge is so subtle that it's barely noticeable. When the sensor in my old car was broken, the gauge stayed at the low end for much longer, but there were no problems when starting the engine when it was warm.

In any case, it currently reaches its operating temperature relatively quickly.
The problem is that almost all of the suspected symptoms only occur sporadically.
Only the sudden increase in engine speed during starting, which practically never occurs during a cold start, is now happening more and more frequently during a warm start.

I think it's best if I check the error memory again and verify the values being reported by the coolant temperature sensor when the engine is malfunctioning.

Regards,

Olaf.

P.S. To Mr. Antje,

I didn't borrow you .
"Still, thank you for the tips. You're generally right that I should first take a closer look at the coolant temperature."

I only checked the thermostat because of the failure to reach operating temperature. If it's working now, leave it alone. However, keep an eye on it and check the reading with VCDS.

Note (again, in my defense regarding the thermostat):
With my vehicle, the speed display showed exactly 90 from 70 up to... Rarely, it would go up to, for example, 80-85, but in reality, it was much lower; it never reached more than 75, and usually less! Anyway, let's first address the main problem.

@Olaf
I had to think about that... You're right, I didn't mean to imply you were "borrowed." I meant "amateur," but I misspelled it and wrote "loan" instead. I'm just a foreigner... Besides, I was completely wrong about the Dyno injection timing; I don't know all the MKB models (or rather, very few of them).

>I meant "layperson," but I wrote "loan" instead. I'm a foreigner, after all...

Oh, I didn't know that. My Dutch isn't very good, so it's probably best if I don't try to speak it.
So far, I've only managed to learn Spanish and English (at least to a level where I feel comfortable enough to start a discussion about spelling).
Basically, it doesn't really matter; the main thing is to be understood.
I think, however, that you can easily ignore that little jab, which was off-topic anyway.

See you then.

Olaf.