A4 TDI: Rough Idle & Troubleshooting

Translated on 18-09-2026, 8:24.

Hello,

Currently, I'm experiencing a problem with my A4 (96 kW, 1.9 TDI, engine code AWX) where the engine vibrates excessively at idle.

Here's what I've already checked:

- EGR valve (blocked and sealed)
- Tandem pump (pressure at 1500 rpm approximately 4.5 - 5 bar)
- New diesel filter.
- Compression: 29 bar, 30 bar, 30 bar, 29 bar.
- Dual-mass flywheel (no noise or play when rotating forward or backward).
(can be determined by the engaged 5th gear).
- MWB 13: approximately -0.52, +0.52, -0.38, +0.38.
- MWB 23: approximately -6, -12, -8, +5.

Where could the problem be?
What values are typically expected in the MWB (Motor-Wideband) sensor when the engine is idling?
How can I safely inspect a dual-mass flywheel?

Thank you very much.

Translated on 18-09-2026, 8:26.

Hi B4!

Please enter your VCDS license number in your profile first; otherwise, according to the terms of use of this forum, no support will be provided.

Best regards from Munich!

Translated on 18-09-2026, 8:27.

It is registered...

Translated on 18-09-2026, 8:27.

Is the alternator clutch working properly?

Translated on 18-09-2026, 8:27.

Do the clutch and brake pedal switches work?

Translated on 18-09-2026, 8:27.

Hello,

The posted values from MWB13 and 23 are okay.

Quote:

How can I safely check the dual-mass flywheel?

Unfortunately, it can only be removed by disassembling it.

Perhaps make a video? The MWB 13 doesn't appear to have any major problems.

Best regards, Rainer.

Translated on 18-09-2026, 8:29.

Hello,

I unfortunately don't have the car here right now.

I may have not expressed myself clearly.

The engine vibrates strongly when idling.
Engine speed fluctuations are difficult to detect using VCDS.

Could it also be related to the motor mount (hydraulic mount)?
When I activate the hydrostatic bearing using the actuator diagnostics, the vibrations are barely noticeable.
To my knowledge, the hydraulic accumulator is only activated while the vehicle is in motion.
Is that correct?

What values are typically expected in the MWB23?

A faulty brake pedal switch should definitely be recorded in the vehicle's error memory.
Why would a faulty clutch or brake pedal switch affect the engine's operation?

Thank you.