Test your mass air flow (MAF) sensor, and check your vehicle's volumetric efficiency (VE) with this calculator. This app is for professional automotive technicians, but can also be used by DIY-er's who have their own automotive scan tool. After collecting some data with your scan tool, just enter it into this calculator and find out if the MAF sensor has a problem or if the engine's VE is low.
You can save your calculations for comparison to other vehicles you check in the future. The global database is available to search when connected to the internet. The local database is empty to begin with, but as you save your vehicles you will have lots of good data to search and compare without the need for an internet connection.