Replaced faulty Anti shudder valve / ASV and car is kangarooing / pulsating revs again

Hi folks,

so I have had a long term issue with the car kangarooing / surging / revs go up and down between 1200 and 1900 revs normally worst when down changing and going through a round about or stuck in traffic. The car is a manual by the way.

The inter-cooler split last year so I replaced that, there was a bit of oil coming from the ASV (anti shudder valve before the EGR) so I replaced that with a decent VDO one this week (as per previous post it doesn't seem to need coded!?).

I had been running the car for 6 months with the old ASV unplugged and the Engine Management light on and the car was running faultlessly and was starting well!

Now randomly new ASV on fault codes cleared and its gone back to this surging and slugish but not terrible starting! Argghh how can that be!

I have ordered a new seal for the intercooler to ASV pipe as I wondered if there could be an air leak - however changing the ASV wouldn't have affected that I don't think?​!

Any ideas? I see on the parts diagram for the charged air system there is an item call a pulsation damper, I hadn't been aware of that before should I be looking at it??

I know a few people that have a similar issue and never really solved it after numerous parts being put on the car so realy want to get to the bottom of it!

Any thoughts appreciated!

I think you should look at EGR valve. Check Vacuum lines, give EGR a clean maybe it gets stuck.
Even more if you saw some oily residue coming from ASV.

Thanks I've had a look about and can't see much, it would probably be worth taking it off I suppose to check.

What I don't understand is why the car performs better with the ASV unplugged and without and detrimental side effects such as poor performance / economy / starting etc!

Does anyone know how the ASV operates? Is it variable or jus open / closed and under what conditions?

ASV or inlet manifold flap on diesels serves two purposes:

It is supposed to close if runaway condition is detected.

And main reason is to get enough EGR valve recirculated gasses to inlet and replace more oxygen to reduce temperature in combustion chamber to reduce NOx emissions .
If EGR gives too much gasses engine may struggle for air.
If you unplug ASV it is open and allows air from turbocharger to enter and work kinda properly, but hardly any recirculated gasses will enter combustion chamber.