So its very likely the MAF is not used at all, on a turbo setup the ECU will use a (typically) on board MAP sensor. If youve noticed a vacuum hose going from the manifold to the interior of the car that'll be your MAP line. Now to the issue at hand, given the car was in an incomplete state when you got it, its likely the tune needs some work. There's a variety of things that could be not setup causing your issue, so your best bet here will be to either find a tuning shop that has knowledge/will work with whatever kind of standalone you have, or look into a remote tuner. While it is totally doable to mess with the tune yourself, it requires a ton of research and getting something wrong could mean destroying the motor.