If it's an oiled K&N, don't you have to be careful it doesn't foul / contaminate the MAF?
No Matt, I'm pretty confident not - that's one of the things they address in their FAQs. It can be an issue when you clean and re-oil them improperly after, 75,000, but as long as you follow the instructions properly and use their kit that shouldn't be an issue. I should add MAFs rarely go wrong; people always disconnect them and change them first thing, down a rabbit hole that is more often other issues - a MAF fault code can often be triggered when there's nothing wrong with it too, beforehand. Plus if you disconnect one, chasing that bunny, you will put it an automatic fault condition, masking the real culprit anyway. They get a fault code, disconnect the MAF; the engine runs great because it has fallen back on a table of standard values in the ECU; bingo they think, faulty MAF.
Digging through some old forums, the oft repeated mantra, from some well respected techs, was: 'STOP disconnecting the MAF to chase faults!' The trick with them is, if they do fail - mine is original - then you must replace with OEM. Knock-off MAFs are worse than useless. I specifically paid more for the K&N filter, after reading many reviews and looking at other high flow makes. They have had a good reputation over a long time.
I think I might know what is contributory to the idling smoke when warm, possibly. The dipstick shows an overfill on the oil; I can't see how this could have happened. I specifically bought litre bottles of Liqui Moly, so as I could add the right amount accurately. I flushed then drained for a long time until the drips stopped; and then I added about 3.5 litres (capacity of this engine is 3.8l) checked the dipstick a couple of times; ran it for 5 minutes; checked again. There might be a slight incline down to the dipstick on the gravel carpark, hard to tell. I can only think quite a bit of oil, say half a litre or so, gets trapped in the engine.
In any case, I'm not overly worried nor in a rush to drain some off. I never go over 2.5k revs 95% of the time and very very rarely touch 3K. I was undiligent though in checking other fluids when I serviced it: The power steering was on min and the washer bottle was empty. So I rectified that this morning, overfilled the steering at first - so easy to do, since the max is less than half the full header. I siphoned some off and refilled to the correct max.
I'm in talks with a very reputable tuning company for a gentle economy tune, that may help limit smoke a little too, and add some useful low end torque. I have adapted the EGR this morning. The filter hasn't arrived yet so we'll see with that too.