Performance Issues: Troubleshooting & Solutions

Hello everyone,

I've had my Bora TDI (115 hp) for about 3 weeks now, and I'm experiencing 1-2 problems.

First, I checked the error memory after purchasing the car (from a private seller) and then again a week later: No errors!

Then it started: First, I noticed the drop in power above 3000 RPM. I read here that it might be due to the diesel filter. So, I'll replace it.

The bigger problem is occasional, complete loss of power! So far, it's only happened while driving, and except for one instance (in 4th gear), it's always happened in 6th gear during acceleration. The power completely cuts out, and you're just glad to make it to the next exit (you can maintain speed if there's no hill), and the 'turbo whistling' disappears. After a 'reboot' (turning it off and restarting), everything works normally again.

Error code read (VAG-COM):
1. DTCs Found:
17958 - Turbocharger pressure control differential.
08:00 - Limit exceeded.

Is this one of the issues that are always discussed here? (/viewtopic.php?t=159) Or is it something else? Unfortunately, I'm completely new to this area and don't even know where to find the parts for cleaning in the engine compartment... The good standard manuals ('Jetzt helfe...' and 'Reparaturanl...') don't say much about it either.

I would be extremely grateful if someone could help me quickly, as I'm planning to travel to Frankfurt (from Hanover) this weekend, and I've been getting a 'test' message on my car's display, indicating a problem with a component that's 250 km away, and it's appeared 5 times already!

Regards,

XtSI

P.S. The car was manufactured in 1999.

The difference in boost pressure readings could be coming from the mass airflow sensor, which tends to fail quite often. I've already replaced mine four times at 170,000 km. If everything is fine after starting the engine, but the problem only occurs at a certain speed, it's almost certainly due to the mass airflow sensor.

Best regards, Alex.

Hmm, then it's probably him! He's only ever been seen on the highway, so never below 120 km/h!

I guess I'll probably have to take it to a workshop, or is it something I can change myself?

AMB1980 wrote:

The boost pressure regulation difference could be coming from the mass airflow sensor, which often fails. I've already had the fourth one replaced at 170,000 km. If everything is okay after starting the engine and the problem only occurs above a certain speed, it's very likely due to that. Best regards, Alex

In my experience, one error has nothing to do with the other. However, I am always open to being proven wrong.

Best regards, Rainer.

Unfortunately, I can't say whether the errors are related, but the behavior (only occurring at speeds above 120 km/h) sounds very much like a faulty mass airflow sensor (MAF).
You can replace it yourself; the part costs around 25 euros.
But definitely keep the slip of paper, for warranty purposes }.

25 euros? If I'm not mistaken, you can easily add a zero to that amount to make it correct.

The sudden drop in performance is a failsafe mechanism of the control unit, which can have many causes.

Does the VTG (variable turbine geometry) adjustment work? If it's stuck, it can lead to excessive boost pressure, which can then trigger emergency mode. Check the website; there's a description of the VTG and how to test it.

Best regards,

Jan.

Hello,

The DTC 17958 does not indicate a limit being exceeded, but rather a control difference (otherwise, the DTC would be 17965).
VAG-COM is reporting an incorrect message here.

For this DTC, please check the following:

Wastegate control valve - check N75.
(N75) is defective; perform actuator diagnosis using VAG-COM.

Hoses connected incorrectly, not properly attached.

"Air leak between turbocharger and..."
Engine (charge air path/intercooler system)

Turbocharger failure.

Before you proceed to the LMM, please check the points mentioned above.

Hmm, I need to find some time tonight to test things out. Yesterday, while looking for the mass airflow sensor (how do you actually get that clamp off???? I'd really like to verschandeln it, it can't hurt, right), I took a look at the air filter and quickly replaced it with a washable one (I've never seen so much sand and leaves). However, the next 250 km of test driving showed: it definitely wasn't a problem!

I wouldn't suspect reversed hose connections, as the problem appeared quite suddenly and recurs intermittently. The previous owner would have likely encountered the issue before if that were the case, and it wouldn't be happening more frequently now.

At first, I thought the problem was speed-dependent and only occurred at higher speeds in 6th gear. However, yesterday, while in 3rd gear at 3900 rpm, I was almost thrown forward.

Can I assume that as long as no error message appears on the instrument cluster, I won't cause any further damage by driving the remaining distance to the next parking spot? Surely, if there's a serious problem, something should start to light up, right?

Regards,

XtSI

P.S. Also, yesterday I also noticed that the tachometer briefly jumped during the period when the engine wasn't producing power (it went down to 500 RPM and then recovered). Apparently, this is a fairly common problem, but could it be related? Well, I'll test everything again today.

'Air leak between turbocharger and...'
Engine (charge air path/intercooler system)


Possibly, that was it! Yesterday, after the error occurred again, I drove out for a 'reboot,' and a turbocharger hose burst! At least, that's what the workshop told me, where I painfully dragged the car. Tomorrow, I'll get the car back, and then it will be shown whether a defective hose was also responsible for the previous problems. I don't think the mechanics will accelerate in 6th gear on the highway during the test drive, even though I pointed it out (I probably shouldn't have locked the DVD player and the radio ).

I'll let you know how it turns out. The workshop estimates the cost to be between 80 and 100 euros at the moment.

Regards,

XtSI

For theoretical discussion only, wouldn't it be advisable to stop driving the car and have it towed instead of continuing to drive it if there's a defect in the system that pressurizes the engine?

The turbo is practically no longer producing any pressure and is running 'empty' at its maximum values, while the VTG (variable geometry turbine) with its most aggressive setting only causes the turbo to whine even louder.

Or is it less significant, and can you still drive a few more kilometers to the nearest workshop? (Which, personally, I wouldn't do based on my gut feeling.)