Engine RPM Fluctuations & Cooling Fan Issues

Hello fellow TDI enthusiasts,
I have a 1.9L engine with 90 horsepower, an EGR system, and 160,000 km on the odometer, and I'm experiencing three problems with it that I can't figure out.
1.
At 170 km/h, the engine speed starts to fluctuate, and the car wobbles despite being on a flat road and with the same throttle position, always varying by about 3 km/h (constantly and consistently). It's not much, but you can feel it (it's like being on a horse...). Also, it doesn't go above 180 km/h anymore, which used to be different.
2.
'I'm experiencing a problem where, regardless of how warm the coolant is (90°C), the radiator fan turns on at the second speed setting every 30 seconds (irregularly) and then turns off after 5 seconds. This is a different pattern than the fluctuation in engine speed, so it's probably not the cause of the problem.'
'I've noticed that during prolonged city driving (when the engine is very warm), when I'm stopped at a traffic light (with the clutch and brake pressed), a dull humming sound comes from the engine compartment after about 20 seconds. This sound lasts for about 3 seconds and then disappears. My thought is that coolant pressure might be escaping somewhere.'
I know I'm new here, and I realize this is three questions at once, but it would be great if someone could offer some suggestions on how to further test or alleviate the issue.
Thank you in advance.

Hello,

jensg wrote:

Hello TDI enthusiasts, I have a 1.9L engine with 90 horsepower, an EGR system, and 160,000 km on the odometer, and I'm experiencing three problems with it that I can't figure out. 1. At a speed of 170, the engine speed starts to fluctuate, and the car wobbles despite being on a flat road and with the same throttle position, always around 3 km/h (constantly and evenly). It's not much, but you can feel it (it's like being on a horse...). Also, it doesn't go above 180 anymore, which used to be different...

As always, what does the error memory show?
Air bubbles in the fuel line between the diesel filter and the fuel injection pump?
Have you already replaced the diesel filter?
Is the fuel tank vent working correctly? Try driving without the fuel cap for a test.

jensg wrote:

2. "I'm experiencing a problem where, regardless of how warm the coolant is (90°C), the radiator fan turns on at the second speed setting every 30 seconds (irregularly) and then turns off after 5 seconds. This is a different pattern than the fluctuation in engine speed, so it's probably not the cause of the problem."

Do you have air conditioning, and if it's turned on, does the first fan speed setting automatically activate?
In my case, the fuse for the first fan speed was defective, and it behaved exactly as you described.

jensg wrote:

"I've noticed that during prolonged city driving (when the engine is very warm), when I'm stopped at a traffic light (with the clutch and brake depressed), a dull humming sound comes from the engine compartment after about 20 seconds. This sound lasts for about 3 seconds and then disappears. My thought is that coolant pressure might be escaping somewhere." I know I'm new here, and I realize this is three questions at once, but it would be great if someone could offer some suggestions on how to further test or alleviate the issue. Thank you in advance.

Do you have air conditioning?

Best regards, Rainer.

'The error memory showed no errors. The diesel filter is 10,000 km old and has been drained, with no air bubbles. I have a Climatronic system. I will try your suggestion about the fan, thank you very much.'

Hello Jens,

Quote:

The error memory showed nothing. The diesel filter is 10,000 km old and has been drained, with no air bubbles.

Okay, that's already a statement. If your vehicle doesn't produce any soot at full throttle, I would next recommend having the boost pressure measured at 3000 min{-1} ^{and full throttle, as well as the readings from the hot film air mass sensor (HFM).
Compare with.}
[url]http://www.dieselschrauber.de/Solldaten_Main.html and pay attention to adhering to the specified constraints!
"The measured boost pressure seems acceptable, but the HFM values are below the target. It's worth testing a known-good HFM (a relatively expensive component, but can be swapped between two vehicles in about 5 minutes)."

Best regards, Rainer.[/url]

Hello Jens,

I'm very happy to see another forum member with an AGR engine. I'm especially interested in your boost pressure and mass airflow readings, as I think my engine suffers from a slow boost build-up.
It would be great if you could log the boost pressure in 3rd gear at full throttle, starting from approximately 1200 RPM and going up to around 4400 RPM.
The corresponding LMM values would also be very interesting to me as a benchmark.

I'd also like to know which vehicle your AGR engine is installed in. Is it perhaps also an A3? Then your top speed seems really low to me. It should be running at least 200 km/h according to the speedometer, right? What was it like for you at the beginning?

Regards,
Alex.

Hello Alex,
Unfortunately, I only have a Golf 4, and I don't have the ability to log data while driving. I always have to go to the VW service center for things like reading error codes. I'd like to get one of those devices, but I'm a mechanical engineer, not an electrical engineer, so I can't solder anything myself. Do you have any recommendations for someone who builds and sells these kinds of interfaces? The professional version from DRV is too expensive for me.
Okay, so, I mean that the car used to be able to reach 200 km/h on the speedometer, but it can't anymore. Do you also experience a 'dip' in power around 4000 RPM, which makes overtaking quite uncomfortable? Of course, it could also be related to the other problems, which is why I'm posting here. But it's nice to be able to exchange information. I'll keep you updated; if I can get some data on boost pressure and mass airflow, you're welcome to have it.
Best regards, Jens.

Hey, I'm also a machine builder.
"This thing is actually really simple to build; just take a look at the schematics here. You don't even need to have any prior knowledge. The parts are quite cheap (in fact, we had all of them in stock at the company, so I even had a capable intern solder them for me for 10 euros – I'm just lazy...). If you need a proper OBD connector, let me know; I'll try to find my second one."
Matthias.