Bro, we are talking about diesel la... Performance air filter doesn't give much improvement (or shall i say u can hardly feel the difference). Reflash ECU only when u get into serious mod on diesel engine. Diesel engine are not the same with petrol engine.. No extractor or exhaust manifold
Diesel = EGR > Turbo > Outlet (Waste gas) Go for High Flow / Free Flow filter when your truck is chipped, that only help because the tuning kit will remap the mass air flow to allow more air sucking, fuel mapping to let the commonrail inject more diesel. There's huge difference after chipping your turbodiesel. That's why chipped turbodiesel tends to smoke alot. Smoke alot in diesel = fuel and air is enough.

Bro, i am not joking. We all know diesel engine runs with Air Filter. Huge difference bro? Why not u get over my workshop and i show u the difference between K&N filter with my stock filter with my stock MAF sensor?

Huge difference? Like how? faster acceleration like 1-2 sec off the stock? For me, huge difference, NO. Better air flow = Yes, but useless if your MAF still allowing the same air flow setup to be flowed in.

Before fitting an K&N filter, power delivery was smooth and eagerly to rev until redline.

After fitting K&N, power delivery was so poor. 800rpm > 2k = no pull at all, and it consume more time to reach 2k rpm for my turbo to boost, once it reach 2k rpm, the boost came and it will hit the redline like normal did ! I was like you back then, refuse to believe. Tried resetting the ECU by disconnecting the battery for 15 minutes (but i left it for a few hours). Clean the stock MAF sensor.. And all what i've did is futile, it's still the same until i remove the K&N and replace back with my stock filter.

Most of the diesel nowadays runs on strict MAF sensors from vary manufacturer like Bosch,Pierburgh,Hitachi and etc.. so putting a high flow or free flow won't work much because it's the MAF sensor controlling the air flow. It's all the same on all commonrail diesel that runs on MAF. But mine run like this, still don't believe? Get over here and test drive mine and i'll prove you so wrong ! I even sent an complain to K&N, guess what they don't even dare to reply my mail at all after a second reply from me !

Try taking off the MAF sensor from any commonrail diesel engine, and see if the engine will rev.

I, myself of course know that diesel engine run on high compression, that is why diesel tends to have better FC than petrol engines, and lower redline compare to petrol engines.

Yes, air is important in diesel engine, but fuel is important too ! But since commonrail engine has enough pressure in injecting fuel to the engine, what those tuner need is trick the commonrail sensor to inject more fuel.

Thus that's why tuning kit / tuning box is introduce to nowadays commonrail engine, what they did is override the ECU reading on the MAF sensors and Commonrail sensor. They trick on them to suck more air and inject more fuel, hence faster acceleration, more torque and more smoke.

Black smoke coming out from diesel = tuner problem? Depends actually, if tuning is done right and no damage on the injector, PCV valves and turbo, IT SHOULD SMOKE more than stock. That's indicating sufficient of air and fuel.

Black smoke on turbodiesel may be symptoms of having clogged PCV valve, faulty MAF sensor, faulty injector and faulty turbo actuator/wastegate. These are the major problem. Also, not replacing the diesel filter for long time will cause black smoke on your diesels too !

All of my tuned turbodiesel smoke and they smoke ALOT if you did an hard acceleration from standstill !

p/s: not everyone will go and tune their stock ecu to run rich / lean... There's no need to ! It's completely different with petrol engine, so stop comparing ! On diesel engine, it's all air and fuel matters !!

Commonrail diesel nowadays run on EGR. Exhaust gas > EGR > Turbo > Engine. (Not happening on your Pajero since you don't run on EGR)

I understand the working concept of wastegate / actuator, hence i don't need to waste my time explaining here.

Diesel cars with extractor? Bro, i'm not joking and i found non of them in my Rover 75 CDTi, ISUZU DMAX 3.0 Ddi ITEQ, Rexton RX290 and my previous Isuzu Rodeo.
It's call exhaust manifold if you're talking about diesel engines, not extractor which u find on petrol engines. Dieselhead mod their manifold probably due to upgrading their turbo !

In case you don't catch my words, here's the pic for your ref:


Extractor on petrol engine:


If i'm not a diesel-head, i wouldn't have 3 commonrail in my car pouch right now.

So far one of my commonrail is up to 75% mod. Air intake mod to allow more air to flow in easily, tuning kit, replace stock Bosch MAF with Pierburgh, replace uprated PCV valve, decatted exhaust, EGR removed and installed a Bypass, uprated o-rings for the intercooler, aftermarket Jetex high flow air filter (order along with new MAF sensor and tuning kit). I did it all myself. It's a commonrail anyway
I'm not proving i'm a pro or anything, as i'm still learning from all the sifus oversea. Talking about modern commonrail diesel?   
I noticed u owned a old mechanical fuel pump Pajero, which is not commonrail.  If that's the case, you might be right in certain point, because i'm speaking of commonrail engine here.. Commonrail vs not commonrail, now that's huge difference as they are completely different technology.. Like those diesel forklift we did, difference is they don't have turbo.