Judging from previous posts, the NMAF is a very sensitive device.
There is a writeup here about testing it : http://www.autoshop101.com/forms/h34.pdf
I will do a summary for you from the manual. It is from page EG-183 for 1996 LS400.
PASSIVE TEST:
Resistance goes down as the temperatures go up. For normal temperatures (20 C / 68 F the resistance should be 2-3 KOhms.
This resistance is measured between the THA and E2 pins.
When looking at the male end connector while MAF is still on the car,
THA is third pin from the left
E2 is second pin from left.
ACTIVE TEST -
--> Connect volt meter, positive to VG and negative to EVG.
When looking at the male end connector while MAF is still on the car,
VG is fourth pin from the left
EVG is first pin from left.
--> Turn ignition on, blow air into the MAF.
--> Voltage should fluctuate.