MAF is Mass Air Flow. There is a meter ( the tube part that is after your air box or conical filter, which ever you have) They come is various sizes geared toward your engines performance. One popular size is 76mm , there is 90mm, 73mm etc.... Then there is the sensor (black plastic electronic device mounted to the MAF meter.
Basically this is your MAF system. Consists of MAF meter and MAF sensor.
There are two kinds of after market MAF systems
C&L (which I have) makes a MAF meter which has a sample tube in which you can change to match your injector size. You use your stock sensor with this meter.
Pro- M Granatelli Motorsports MAke a MAF Meter and sensor combo. Their sensor is electronically tuned to your injector size.
My sensor went bad, perhaps from cleaning is with o2 safe throttle body cleaner. Only clean your sensor very carefully with quick dry electronics cleaner or very very gently with alcohol and a swab. This information is directly from an A-1 certified mechanic. He said I ruined my sensor by using the throttle body cleaner.
Below is a post I read on AFM about HOW TO CHECK IF YOUR MAF SENSOR IS WORKING OR NOT ( it also tells how to check if your IAC is bad ,which is your idle air control)
I found this post and I found that my MAF sensor is bad. It started and idled no problem with the maf sensor unhooked.When I plugged it back in it died.
Please read it. It was so simple and it makes total sense.
Ya know, I just did a bunch of mods to my mustang, but it all started from changing out the intake manifold, upper and lower. Well mine would not idle too, I called ford
and they told me to try two things.
Unplug the IAC (The tubular looking thing on the right side of the throttle body if your lokoing at it FROM the passenger side), with it unplugged try firing up the car, it should have an idle assuming the IAC is bad (so ford said). If that doesnt work, plug that back in and unplug the MAF sensor and try firing the car up. This is my problem. My car will not hold an idle, or even run, and has horrifying throttle response, and I discovered that with the MAF sensor plugged in, my car would crap out...so I unplugged and sure enough the car had an idle. Very rough idle but it was running, and while it was idling I plugged the MAF sensor back in and bam, the car died on me. So i'm getting it replaced, hopefully that solves it. Try those two things, unplug your IAC and fire it up, if that doesnt work, plug it back in, then unplug the MAF Sensor and fire it up, that doesnt work, unplug them both and try it. Beyond that, I dont know. :-\ Maybe a vacuum leak? Anyways hope this helps.
Here are some links with pictures on MAF Systems http://www.cnlperformance.com/images/76installed.jpg http://www.cnlperformance.com/maf_86-93.html http://www.granatellimotorsports.com/
Hope this helps