Okay I have a 1996 ford aerostar I got a code p0171.. so far I get it's a has to do with m.a.f. mass air flow.. the o2 sensor test fine.. so I know its about 200 buks for new m.a.f.how do I test it ? Can it be tested ?to make sure that's what I need.. thanks

Cleaning the MAF Sensor will likely solve the problem:

https://www.askmehelpdesk.com/cars-t...ml#post1377134

Afterwards, clean the air box, wipe it down with a damp cloth, allow it to dry, and install a new air filter.

If the MAF was the problem, you should be getting the P0171 (bank # 1 lean), but you would likely also have a P0174 (bank # 2 lean).
If cleaning the MAF doesn't work, check for a leaking intake plenum or perhaps a leaking intake gasket.