Limp mode/black smoke

G'day folks,

I know this question has been asked plenty of times before but I can't find anything exactly the same as mine, so I'm asking again, appreciate the patience!

GU 2009 3.0l

Symptoms:
- Black smoke, when accelerating. When going downhill and revs below 2000 nearly no smoke at all but going uphill and any revs over 2000 and it kicks out quite a late of black smoke, even when holding revs at a set rate for an extended period.
- Limping. Accelerates fine until you hit 2400 then suddenly drops back to 2000, then climbs normally to 2400 then drops to 2000. But if you really push your foot down so it drops down a gear it'll let you accelerate as normal.
- Takes a while to start each time, maybe 5 seconds (quicker if it's hot).

Things I've tried:
- Put a new MAF sensor in. No change.
- Changed air filter. No change.
- Tightened intercooler hose clamps. No change.
- Injector cleaner diesel additive. Only done half a tank with the stuff in, as of yet no change.
- Have disconnected the battery just then, will leave it unconnected tonight.

Is it possible a dodgy tunit chip would be the problem? Can I simply unplug it and run the car to see if it changes anything or is there more to disconnecting one than that?

Just wondering if anyone has any other thoughts, or things I should try if it's still doing it tomorrow.

Trying to sell it so would like to get this sorted!

Appreciate the help.

check the back right hose on the ic mine popped off on a trip and blew black smoke
no power, check what boost you are running to. Do you have an aftermarket IC.
Try anything you want but only do one thing at a time like disconnecting the chip

I would definitely by pass / disconnect the chip first and see what happens. Start there and then eliminate further if need be.

Wot he said ^^^^

Black smoke = shitty injectors/excess fuel/not enough air.

Now you have disco'd the battery to force an ECU relearn the next step should be bypass the chip.

I assume you don't have a Scangauge or Boost gauge to rule out the 'not enough air' ?

Thanks for the replied everyone. I think I've narrowed it down to faulty MAF wiring. Reconnected battery, did nothing. Disconnected chip, did nothing.
Got my voltmetre onto the MAF wiring and from what I can gather from reading other posts it's not working properly. The white wire was reading the same voltage as battery (roughly 14.2V while engine running). The next wire read 0V as it's supposed to apparently. But the next wire also read 0V where apparently it's meant to read between 1.5 and 1.9.

Does that sound like the standard 'wiring fault'?

I think I read somewhere that the MAF sensor runs off an ECU relay? Does anyone know which one that is on a '09 GU IV?