testing MAF sensor

99 4.0 engine 4x4 .Can anyone tell me if there is a bench test for the sensor. I have codes po171&po174,I have been searching for a vacuum leak ,no can find.The hoses all seem fine. Tried spraying DW40 but I'm not sure I'm hitting all the right places to test:banghead: .From all the reads in the forum it comes back to being a leak.This all started after I changed the thermostat,I've checked and rechecked the hoses.
I just wondered if I could test the MAF to eliminate it as the problem.I have cleaned it and the air filter.

Can't help you with the MAF test, but I have the same codes.

I have no symptoms other than my gas mileage may have dropped off a little.

I'm replacing the O2 sensor tomorrow.

I'll be watching close in case that doesn't do the trick.