What year was the car you got the MAF from? There are a couple of different MAF's available depending on what year the car is. I am pretty sure they are not interchangable.
If you haven't joined RennTech yet, there is a good DIY on how to check the MAF for proper operation.
http://www.renntech.org/forums/index.php?/tutorials/article/200-maf-basic-test/