"A rule of thumb on a MAF's air flow rate at 500 rpm is 1 gram per second per liter of engine displacement."

This rule of thumb only works for an engine that has relatively no load on it, e.g. no A/C on and no heavy electrics (like cooling fan). So since you have a 3.0L engine, that means at 1000 rpms, you should be seeing about 6 g/s of air being reported by the MAF. This is the easiest to do with just the throttle. Then you can check it by then rev'ing slowly to 1500 rpms, 2000 rpms and record what readings you are getting. This should follow a linear fashion, so you can also interpolate data if you are running at say 700 rpms or something in between.

Obviously there will be pumping losses and and friction involved, so more likely than not the mass flow rate is going to be slightly higher.

Make sense?

__________________
2003 BMW X5 3.0i -- MT5, 3.64s final gears, H&R lowering springs, K-Mac bushing kit
2007 BMW X3 3.0Si -- MT6