How to eliminate diesel clatter 3.0tdi CDUC & CDUD 2nd Generation


Registered User
Apr 22, 2018
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Hi All
Thought I’d share this with you in case it helps someone......
Has any 3.0tdi CDUC, CDUD owners who have higher mileage engines notice a more pronounced diesel clatter noise at idle or at low rpm and maybe notice the engine isn’t quite as smooth in low rpm as it used to be ?.
Here may be your solution?.

I was desperate to find the solution to this issue and did everything, new injectors, Maf, egr and Dpf cleaning. None of these really worked and it annoyed me that such a nice engine wasn’t as refined as it should be.

By pure fluke I found the answer in 2 words “Swirl Flap”.....

Bear in mind that the older 3.0tdi engines has swirl flaps in the intake manifold. The 2nd gen engines don’t. It has one large motorised swirl flap before the manifold with two holes. One for EGR return and other for fresh air. The fresh air hole has a butterfly valve which opens and closes but mainly it’s a low rpm when it’s used to swirl the air into the intake.
These things fail and can do so without any warning light or error codes. The flap which gets built up with carbon may not be opening properly literally starving the engine of fresh air and too much EGR gases.

Quick solution is remove the part and remove the butterfly valve, it’s only two screws and the rod can be left in situ so no error codes are thrown when plugged back in.

Before removing the butterfly valve you can make a quick test. Unlock car open the bonnet, close the door and lock the car. Leave for a minute and disconnect the sensor/motor. The flap will now be fully open and you can test for yourselves if it improves the drivability of the car. It will eventually throw an error code and your Dpf may not regen as a result so if it’s improved I would suggest you remove the butterfly valve.

You may notice at first that the car pulls away a bit more sluggish than normal but the ecu will rectify this after a few 100kms.

The second part was to connect VCDS....
Go to Engine - Adaptation - EGR Correction

Select 35 mg/stroke as new value. Old value should be 0mg/stroke. This will close the EGR valve more and effectively tells the Maf to read higher fresh air intake you will probably see around 350mg/ stroke at idle with this adaptation. It’s within the parameters of the ECU so no harm will be done.

Guys give it a try if you think your engine is sounding a bit clattery.
Would be good to get some feedback if you try this yourselves.