1.6HDi lumpy tickover

[freddyokel]

My 207cc 1.6HDi has developed a kinda lumpy tickover.
It dips every second or so and then recovers. This continues until it is warm. At which point it becomes almost undetectable.
I've had the intake system up to the turbo off a few times recently for other things so I'm suspecting unmetered air entering from the connection to the PCV valve as pushing it back hard appears to make it happen less.
Does this sound... reasonable?
I've got a new (larger) O-ring to put on the side pipe from the turbo inlet pipe and, a new PCV cap, diaphragm and spring.

[mickthemaverick]

That type of issue with tickover more often than not turns out to be a vacuum leak or induction system leak so I would think you are on the right track!

[freddyokel]

Replaced the O ring with one recommended on another forum, 19x4mm.
Very tight to get on and very tight to get the spur tube from the inlet hose back into the housing on the rocker cover.
But...
Tickover is now rock solid.
Only dips in tickover I've seen were during the roof manoeuvre when the roof is at it's highest and just before the windows go back up, which is when the current drain on the alternator is at maximum.
Reported fuel economy has also jumped by around 5-10%.

[mickthemaverick]

Excellent, well done, sometimes it still amazes me what a tiny leak can do to modern engines!!