1Z: Performance Issues & Error Codes 0527/0575

Hello to all you TDI enthusiasts out there!

I'm asking for your advice on behalf of a friend of mine.
First of all: The 'patient' is an Audi 80 1.9 TDI 1Z with 165,000 km on the odometer, and it doesn't consume any oil.

The following problem has occurred with the car:
'In 5th gear, starting around 140 km/h, there was a sudden and relatively significant drop in power. Some black smoke (exhaust) was present, but only slightly.'

2. At a constant speed in the low RPM range (approximately 2000-2500 RPM) and with a consistent throttle position, there is significant black smoke coming from the exhaust. However, if you press the accelerator more, the black smoke almost completely disappears. The idle is perfectly normal.

3. Relatively noticeable noise when accelerating. It likely originates from the intake area and sounds like a loud rushing or hissing. The noise occurs across the entire RPM range, as mentioned, during acceleration.

According to the VAG-COM analysis, the error memory reports codes 0527 and 0575.

5. There is a slight oil leak somewhere in the intake area, likely an oily mist that spreads throughout the engine compartment (but as mentioned, it's not very pronounced).

That's my description of the problem; I suspect there might be a leak somewhere between the turbocharger and the intake manifold (perhaps a crack in a hose?).
Could I be right with my guess, or is there a hot tip about what it might be instead?
Or, what tricks are there to find the defect?

I am grateful for any response.

Best regards, Flo.

Hi,

It sounds very clearly like there's a leak in the pressure area, as you suspected.

In these hydraulic hoses, a slight oil mist is normal due to the design. If this mist appears, you've almost certainly found the leak.

I once had a leak in my cooling system that was about 0.5 x 0.5 cm in size, and I found it like this:

The oil mist indicated the direction, and the location of the leak was then determined by intermittently applying gas while idling and simultaneously searching in front. While the boost pressure hardly increases when stationary without load, the turbocharger provides enough air to make the escaping air very noticeable (it's actually pushed out forcefully).

Okay, do that and then seal it, replace it, or secure it, depending on exactly what's broken.

It is unlikely that you will be able to produce the hissing sound under normal conditions without applying any load.

Best regards,

Jan.

Hi Flo,
The errors have approximately the following meaning:

527
Intake air temperature sensor (G72).
The wire has a short circuit to ground or an open circuit/short circuit to positive.
Either there's a short circuit in the power supply line or the sensor is defective.

575
Suction pressure regulation differential.
Faulty hose connection.
Defective turbocharger pressure sensor or...?
The N75 boost pressure control valve is malfunctioning.

Since you have VAG-COM, find the relevant tables from the 'Troubleshooting and Instructions' section and compare the actual values with the expected values.

Best regards, Rudi.

Hello,
Here's a small additional note from me:
I'm just wondering why the power loss only occurs at a specific load or RPM, and why it appears suddenly. If there's a leak in the intake manifold, wouldn't the power loss be noticeable to some extent across all RPM ranges?

Could it be that the pressure loss due to a leak only falls outside a certain tolerance range when operating under specific conditions (e.g., high-speed highway driving), and that the intake manifold pressure sensor only detects an error at that point, causing the engine control unit to switch to limp mode? This could explain the sudden onset of power loss (which would then not be directly related to a leak in the intake system, but rather to the limp mode).

Could I be right with my assumption?

Best regards, Flo.