ka24de maf sensor prob?

Hey guys,
a question for my friend that myself or anyother of my 240sx buddies can figure out. He got the car a few weeks ago and it runs fine. when he takes off the air box from the maf and starts the car it won’t idle right or respond to throttle. Even when the vibrant maf adaptor is bolted on with k&n filter it won’t run. It will run with the upper air box on only or the full tock system in. Is this a bad maf reading or what. I know lots about technical things with 240sx but this has got me stumped. What do you guys think or experienced? Thanks guys in advance.

… are there any vacuum lines being left off?

I had a similar problem, turned out the maf to air box connection wasn’t tight enough.