A3 (ALH) Power Loss: Causes & Solutions

Hello everyone,

Currently, my A3 is giving me quite a headache. It's an ALH engine with 66 kW and has a mileage of 98,000 km.

The performance loss started gradually; the maximum speed became lower and lower, and the acceleration was noticeably reduced.

Currently, the car is reluctant to accelerate when under load, and achieving a top speed of approximately 150 km/h on flat ground now requires considerable effort.

When accelerating, the power drops rapidly and noticeably from 3000 RPM onwards.

Air filter is new.
The diesel filter is new.
Fuel line is tight, no leaks or bubbles.

When using the diode as a replacement for the mass airflow sensor (MAF), the actual value read was 1275mg, which caused the engine to produce excessive soot and have a rough start. When accelerating while stationary, the engine also took some time to reach the desired RPM, requiring repeated adjustments, so I refrained from conducting any test drives out of caution.

During the test run (with a mass airflow meter), it was observed that the desired boost pressure was achieved 'normally' (with a brief, very slight overshoot). The target and actual values are nearly identical; the boost pressure builds up shortly after the start of acceleration and remains stable throughout the entire period without any drops.

However, the actual amount of air mass remains far below the target value (target: approximately 800 mg, actual: 420 mg).

I haven't checked the fuel injection values yet while driving, but I will do so later. However, since the car isn't producing any black smoke, I believe the values are being adjusted based on the air mass. I'll provide those details this evening.

I removed the EGR valve earlier and inspected the intake manifold. It has a layer of soot/oil buildup, approximately 1 mm thick. I didn't remove the intake manifold from the cylinder head.

The crankcase ventilation system is working properly.

The exhaust system doesn't sound particularly unusual (I recently had a broken catalytic converter on my parents' Passat 3B AFN). The exhaust flow is pulsating at idle, so I don't see any signs of a blockage there either.

CONCLUSION:

What should I do? I don't have a suitable mass airflow sensor (MAF) to swap in (although there are three TDIs here, they all have the 'old' connector on the MAF). Right now, I also don't want to remove the intake manifold to check the continuity/cross-section of the channels.

Best regards,

Jörki.

Quote:

When using the diode as a replacement for the mass airflow sensor (MAF), the actual value was 1275mg, which caused the engine to produce excessive soot and a rough start. When revving the engine while stationary, it also took some time to reach the desired RPM after several attempts of overshooting and undershooting, which is why I cautiously refrained from conducting any road tests.

Then you could have avoided the whole thing .

Sometimes, it only takes a little bit of motivation .

Hey Rainer, just wanted to say thanks again for the 'nudge' (hint). I was just on the highway, 4 km each way; going there with the LMM (likely referring to a mass airflow sensor), and back using the diode. The car sounded terrible and scary around 1500 RPM, but after that, it drove like 'before.'

Therefore, I'm going to order a new mass airflow sensor (MAF) tomorrow from the parts store because I think it's likely the cause of the problem; I can't imagine it being anything else.

I've logged in and out a couple of times. I can gladly refine the charts further and publish them online.

Thank you again.

Jörki.