How to Refresh/Modify your Air Flow Meter
While this is a relatively simple and straight forward set of procedures there is, as always, room for error. I can not and will not be held responsible for any damage done by any person using the information contained in this write up.

That being said, the following prodcedures really are very simple and can provide a world of difference in the driveability of your factory fuel injected Z. Now not all results will be the same. Some Air Flow Meters (or AFM as they will here after be known as) may not need to be recalibrated or adjusted at all. Others may need to be replaced altogether. But the information I am about to disclose to you is basically what you would be paying to have done if you were to have your AFM rebuilt.
Locate the AFM.
The one on the left is from an 83 Turbo model. The one one on the right is from an 81 Non Turbo model. I've opened other and all are basically the same.
If you dont know where it is or what it looks like then maybe you should skip this write up. But if you insist then it's located in the front left side of the engine comparment
Clean It
I realize this isn't the funnest thing to do but if your AFM is over 20 years old and has never been so much as wiped out then there is bound to be some crud in there. Mine was pretty filthy before I cleaned it up. Don't ask me how it got that way but it was. This is a look at the after effect. I may even try polishing it if I get bored enough. The little plastic piece sticking out on the side there is the Air Temperature Sensor (or ATS). It is a very important sensor and should be clear of any dirt or grime. Becarefull not to damage it though.
A Paper towel or a cloth should get most if not everything out from inside  your AFM. If not then a little brake cleaner will help. I recommend brake cleaner cause it evaporates quickly and it doesn't leave any kind of greasy residue behind. After you spray it with brake cleaner go ahead and wipe out anything left over.
The connectors
This could quite possibly be the most important of all the procedures. Cleaning the electrical connector on both the AFM and the wiring harness is VERY important. A corroded or dirty connection could very well be the cause of all your AFM related problems. People will go through all the trouble of opening up their AFM's when all they really needed to do was clean up the connectors.
The time it takes to do this varies. Some connectors are heavily corroded. Others dont need any treatment. Regardless a little touch up is a good idea.
Here's the procedure I use to clean up the connectors. First you need to take a trip down to Walmart, hardware, or autoparts store and pick up the following: Electrical Cleaner (try to get the kind designed to clean up corrossion), an eyeglass repair kit (you'll need the little flat head screwdriver. Skip this if you already have a tiny flathead. You can also use a razor blade),  and some dielectric grease.

The first thing you need to do is locate the connector. It's on the underside of the AFM. If you removed the AFM from the car (which you should have) then you should already know where the harness connector is.
Now take your electrical cleaner and spray down the connector on the afm and also the one on the harness. Not too much. Just enough to soften the corrosion. Let that soak for a moment and then get out your little flat head screwdriver. Now start scraping the corrosion off of the connectors. Then give it another spray with the cleaner and let it dry. Use a paper towel or cloth to get out any loose debris that is left behind. You dont need the dielectric grease just yet.
Opening the AFM
Now comes the fun part. Getting the case open. It's not difficult, just don't gouge yourself while attempting this. I use a flathead screwdriver. You can also use a a razor blade or what ever you find suitable. The lid, pictured at left, is held in place with a silicone sealant. This sealant must be seperated from the lid. Simply insert the tip of the screwdriver (or whatever you're using) and slide if firmly along the perimeter of the case making sure you're cutting the sealant and not riding on top of it. Once you've made a couple passes around just pry the lid off with the screwdriver. This part
can be stubborn but it WILL come off. These lids aren't delicate so dont be afraid to pry. Just don't over do it. If in doubt cut around the edge again to make sure you got all the sealant.
The AFM pictured on the left is from a 83 Turbo model. The AFM  on the Right is from a 81 Non Turbo.
Here's the breakdown on what all the pieces inside of the AFM are.
1: Set Screw for spring tension retainer.                         5: Circuit Plate
2: Spring Tension Retainer.                                           6: Air Temperature Sensor
3: Flapper Door Counterweight.                                     7: Spring Tension Adjuster Cog
4: Carbon Track                                                           8: Flapper Door Tension Spring
Adjusting the Carbon Track (4)
Please refer to the above pic for reference as to what part I'm talking about and where it is located.
The carbon track is basically a resistance field. As the swiper arm slides along the carbon track it sends a signal. Based on where it is on the carbon track and different resistance is used to help the ECU determine the position of the flapper door.

The problem is that over time the swiper arm can wear grooves into the carbon track. You can see the two parallel lines (marked as grooves in the pic) that follow the swiper arm path.
The reason those grooves are a problem is that they can cause the swiper arm to lose contact with the carbon track either partially or completely. Either way, the resistance is varied and the signal is changed. So that the ECU is reading something it shouldn't be. This can severly affect drivability. So what we're going to do is give the swiper arm a fresh path to travel along so it sends a good signal at all points of its radius.

We're going to do this by moving the circuit plate slighty. Alls thats needed is less than 1mm of a difference in location to give the swiper arm a new path to travel. Heres how it's done:

First you'll need to loosen the 3 screws that hold the circuit plate in place. Only loosen them slightly. You dont want the plate moving around on its own. And you dont need to remove them.  Now we want to push the plate up toward the casing (up is refering to the picture above). DO NOT move the plate side to side or the swiper arm can come off the track at some point. You only want to move the plate just enough so that the swiper arm contacts are no longer traveling in the grooves. Less than 1 mm is adequate. Now tighten the screws and push the swiper arm through it's swing radius and make sure that it at no point intersects the old grooves or comes off the black carbon track. This is important. If it does either at any point then driveability will suffer. Once you're sure then double check that the screws are tight and this step is finished.

NOTE: If for some reason you can't move the plate far enough up then try moving it down. If that still doesnt give you enough adjustibility then you can use a file and enlarge the screw holes. Just make sure the carbon track is properly aligned side to side. That is far more important than top to bottom.
Now it's time to reinstall the AFM back into the car. But you have two choices here. You can either apply a fresh bead of silicone and seal the AFM back up or you can leave it open and move on to the following procedures. Your call.

This is where the dielectic grease comes in. Be sure to use it to seal up the electrical connectors so as to keep moisture out which will in turn keep corrosion at bay. This will ensure your AFM works correctly.
If you don't own an air/fuel ratio guage then I wouln't recommend carrying on with the following procedures as their purpose is to adjust the air fuel mixture. If you're into trial and error or have the strange ability to sense air/fuel ratios then by all means carry on. As always, performing the following procedures is done at your own risk.
The Idle Mixture Adjustment Screw is located on the lower side of the AFM near the Inlet. See the arrow in the picture at left. Not all AFM's have this screw however. All non turbo models should, but some turbo models may not. If you won a 280zx Turbo then go ahead and skip over this procedure.

What the screw does is meter the amount of air that is allowed to bypass the AFM. Since this amount of air is such a small amount it really only affects the air/fuel ratio at idle.  This works becuase while the flapper door signal is telling the ECU that only 'X' amount of air is getting in, the  mixture screw is allowing more air to bypass. This in turns leans or richens the mixture depending on screw position.
To adjust the mixture all's you NEED is a flat head screwdriver. But you really should have an air/fuel guage hooked up to the car. The screw is supposed to have a plug over it but over the last 20 + years it's bound to not be there. But if it is just pop it out. Now with the flat head screwdriver you simply turn the screw in the direction needed to correct your mixture.
Clockwise = richer
Counterclockwise = leaner

The reason is that as you turn the screw clockwise (tighten) you close the air passage and let less air through. So the mixture becomes richer. If you turn the screw counterclockwise (loosen) you start to draw the screw out and this opens the air bypass passage and allows more more air through which leans the mixture out.

Thats it.
This mod serves a couple purposes. But if done without the aid of an air/fuel guage can affect driveability negatively. The reason I originally attempted this mod was to lessen the force nessecary to open the flapper door. Which would mean less resistance for incoming air. Unfortunately I was thinking of the impact this would have on driveability.  The spring tension is precisely calibrated (or atleast it was at one point). And messing with the spring tension will alter the air/fuel mixture. The only point at which the air/fuel mixture isn't affected is at WOT. The flapper door can only open so far so at WOT it doesn't really matter what the spring tension is. Here's the breakdown on what the adjusments do and why:

Lightening Spring Tension: This will richen the mixture. This happens because as you lighten the tension on the spring, less and less air is required to open the flapper door a given amount. But mean while the ECU is calibrated to think that the spring is still at it's OEM settings and so will still think that more air is actually flowing in. This will cause the ECU to still dump in it's calculated amount of fuel. But since less air is actually coming in this causes the mixture to richen.

Strengthening Spring Tension: This does the opposite. It leans the mixture, and it does it because it now takes more air pressure to open the door to a given. The ECU reacts the same way as if lightening, relying on it's factory programmed settings, only now it leans the mixture out by adding less fuel. (NOTE: DO NOT, under any circumstance lean your mixture out below the factory setting unless you have an air/fuel mixture meter hooked up. This can cause serious engine damage. A rich mixture will do nothing more than cause driveability issues and maybe foul your plugs. A lean condition can destroy your engine.)

With all that said, here's the How-To.
The Components:
1: Tension Retainer Screw
2: Tension Retainer
3: Tension Spring Cog
4: Tension Spring
What You'll Need:
1: Phillips Screwdriver
2: Permanent Marker
The first thing you need to do is make two referrence marks with your permanent marker. If you look at the picture above you'll see two green lines on either side of the Tension Spring Retainer. This is where you should make your reference marks. This way you'll know how much adjustment you've made and alway be able to come back to your original settings. If you skip this step, you may end up sorry.

Now you'll need your screwdriver. Break the screw loose but dont loosen it yet (some have glue holding them in place). Now secure the tension spring cog in place. You can use a flat head screwdriver, but I just use my fingers. What ever you do, just dont let it go or it'll spin until the spring is competely slack. Not goo. Now with that secure loosen the  retainer screw enough to the point where the cog can be turned. If you want to lighten the pressure then the cog will do all the work. Just let it turn itself. If you want to tighten the spring tension then you need to work against the spring pressure. Then just tighten the screw down and check your results. Check you air/fuel ratio at different RPM's. Once you have satisfactory readings you are finished and you can now seal up your AFM. You're finished. Enjoy your new found driveability.