Rough Shutdown - Im stumpped

[adani24]

Hi all, I noticed this problem about 2 weeks ago. Engine shakes on shutdown - this makes the whole car wobble. I suspected the anti-shudder valve (ASV) , but it is working - I've seen it move quickly to the closed position upon engine shutoff and quickly back open again. I had my son switch off the engine and me watch.

What I have eliminated:

• The ASV has been seen to be working - contacts are ok, there is oil in the electronics but I cleaned that all up carefully and have seen the ASV working.
• All filters (air, oil, fuel, cabin) were changed 10k miles ago (6mths ago), I use supermarket diesel with Millers ECO Boost additive (for about 6months now) Injectors and the like should be clean - engine idle is smooth and mpg is good.
• There are no fault codes - I scanned with my VAG-COM
• I haven't found any split vacuum hoses visible from the top of the engine bay
• The EGR is electronic, The connections are not corroded - I dont know if I can check it's function with the ASV removed (appreciate suggestion on this)
• Today I removed the ASV, EGR, and Air Inlet manifold, gave all three a good clean with carb-cleaner and steam, and put everything back with new gaskets (four in total incl the orange rubber ring on the ASV) and a little copper grease - still the violent shake on shutdown remains.

Some possible causes of the shake:

1. Engine mount? If so, why dont I get a fault code?
2. Intermittant ASV?
3. EGR valve
4. Leaks elsewhere in the charge air system? I'll need to start stripping more of the car to trace the exact location.
5. Anything to do with Pulleys?

Your help greatly appreciated because I am stumped

[Crasher]

Failing dual mass is the most likely reason.

[adani24]

thanx crasher for pointing me in the right direction.
To prove this theory - over the last few days, I've been turning off the engine with the clutch pressed (pedal down). Result: engine dosent shake as hard, its a very significant difference. I've deduced that the engine is shaking much harder with the clutch engaged (extra rotating mass), and much less with the clutch disengaged (less rotating mass).

As it's nearly £800+ for repairs, I can live with some vibrations - upto a point. A slipping clutch will force a decision. According to Audi this is the original DMFW and clutch. I believe that because the previous owner was a Judge who stuck with the same main dealer, im the 2nd owner. I think 170k miles on the original flywheel and clutch is good. But its 11yrs old now and I think might not be worth the spend.

Any thoughts?

[Crasher]

I would leave it until it starts to rattle at idle but I have known them to snap the crank on the 2L, VAG in their infinite wisdom decided to use a cast iron crank instead of forged steel. They don't often fail suddenly but can do so and damage the bellhousing and the debris can get into the starter motor and make it crank slowly therefore causing starting problems with it not reaching the required 280rpm threshold.