Hi everyone, i'm new to this forum and this is my first post.

I have a RRS TDV6 and when its at a constant speed it judders a couple of times and then the power starts to die off and occasional black smokes puffs out of the exhaust when it doing this. I have tried everything i can think of and its still the same. Has anyone had this problem or knows what it could be?
thanks

Could be a split in your intercooler pipes maybe? ON THE WAY: BMW F21 M140i
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checked all the pipes and no leaks, i wish it was that simple

EGR valve possibly. I believe the EGR functions when at constant revs / when power isn't required. If it's failing to close properly then that would cause issues with power and overfuelling (the black smoke). Have you read the fault codes? 2012 SDV6 - it's missing a couple of cylinders
2008 TDV8 - it was a labour of love and is much missed

It doesn't come up with a fault code which is strange, but ive read the actuals on the diagnostics and its showing both EGRs functioning correctly, but ive never had it on when the fault is happening as its difficult to say when its going to happen! it can do it as soon as you pull away or normally it will happen after 10 miles of motorway driving. suppose i should take the diagnostics out and see what the EGRs are doing when the fault is happening ??

Have you tried a cleaning fuel additive?

Yeah tried that, I'm just pulling my hair out with it now

i had the same problem.

a bottle of diesel injector cleaner.
i am 98% sure you will find a split in your intercooler pipe (up the top inside the 90' section) it opens up under boost.
clean the intercooler whilst the pipe is off.
An indication it is the pipe is an accumulation of oil on the bottom of the pipe.

I also did an egr delete and cleaned the "Y" section in the intake manifold.
cleaned the MAF sensor with carby clean.
new air filter.

Runs Like a dream now 245'000kms i'm at.
Sounds like a lot of work but really it's simple stuff.