MAF Problem

Here is my situation: I have a 91 GT, that already had a descent motor in it with an intake swap, shaved heads (believe they're stock), and new cam. I decided to twin turbo the car. The car still had the original 19# injectors in it, thought that was a little small for what power the car had, it seemed to hit a wall around 4500-5000 rpms.

For the first part of the turbo build I bought 38# injectors, matching maf, and adjustable fuel pressure reg. Both the injectors and maf were used. I put all the parts on and it couldn't idle or run. Since it was big injectors, I turned the fuel pressure down to about 20-25 psi and it still wouldn't idle. I then decided for whatever reason to try the stock 55mm maf with the bigger injectors, I had to turn the idle up to about 1,000 rpm but it would idle perfectly fine. I drove it around the block like that, but couldn't get above about 1700 cause it would run terrible. So then I decided the used maf calibrated for the 38#s must not be any good. I put it back on to make sure and it again wouldn't idle, but out of curiosity I gave it gas and it would run smoothly higher in the rpm range, around 2000, where the stock one wouldn't.

So with that description, do you think the new (used) maf is bad? Note: The injectors, maf, and fuel press reg. are the only things I have done to the car.

Also what is the significance of changing the fuel pressure when the car is on as compared to when the car is off?