I'm in the process of rebuilding my AFM from my '91 coupe. As of right now the AFM is under a rotor as weight while the epoxy is curing, more on that later.

A bit of back story. When I bought the car several years ago the car had the typical bouncy idle. It would surge back and forth around 1k rpm. At the time I thought it would an easy fix but it was a no go. I reset the tps, replaced and reset the tps. Messed with the throttle a bit. Nothing fixed it so I left it alone. A few years latter the engine died on me. Broke a coolant seal. The car was and still is my DD and I really didn't have the time to rebuild the engine, so I found a new one. And a new one I found, plus as a bonus it was a complete engine minus a AFM and MAP sensor. I did the swap thinking all my problems with idle would go away.... I did not. The idle continued to do the same surging only now it hovered around 1.5k rpm. so I left it.

Today. or a few days ago actually. The engine decided to go into limp mode, but only part of the time. I checked out the omp and it was good. So I once and for all ripped out the AFM (which I figured was causing the problems) and did some testing with a multi-meter. Just as I thought it was bad. The reading when it was closed was fine (FSM says 200 - 1k ohms) but as it was opened it would jump allover the place as high as 2k.

I did a bit of search and found nothing really here on the forums and didn't find anything about fixing the problem other then replacing the unit. Unfortunately the only options were a rebuilt afm from mazdatrix for roughly 300 or find a used one. After some googling I came across a few videos on youtube ( and ).

The videos are really bad from a instructional point of view but you get the jist of what to do. Here is what I did. The AFM is divided into 3 parts. The front section, has the cone that air flow pushes on. Middle section which holds the potentiometer and air temp sensor. Then the back section that just acts has a housing for the potentiometer.

I only removed the back section (see attached pics). I opened it up with a hacksaw. What you do it cut into the grove all around the afm evenly going only 1/8th to 1/4 inch. Don't keep cutting untill it falls off! After you get a good grove into it, take a flat head screwdriver and pry the end off evenly around the case. If you hear a plastic breaking sound you got it. That is the factory epoxy breaking loss.

What you will see is what I pictured. The cause of the funky ohm readying is the black contact strips being dirty. Even if it doesn't look like it. Mine didn't look bad at all, but it was. Next up is cleaning those strips. I simply used a Q-tip and rubbing alcohol. Just dip the Q-tip in the rubbing alcohol and wipe off the contact strips. Blow dry it off and redo the ohm test. Mine was dead on perfect afterward. That was the easy step.

Next is putting it back together. I went and picked up some loctite epoxy from home depot for 10 bucks. but before using it. It would be a good idea to scrap/cut/grind off all the old factory epoxy off the lip of both pieces first. After I got it all cleaned up I gooed on the epoxy on both lips and put the them both together. Be mindful of the alignment notch on the inner ring around the potentiometer. Also Mazda put a sealant around that ring. Again it would be a good idea to do the same as it should be a sealed area.

As of this typing the epoxy is curing. I stood the afm assy on end and set a rotor I had siting around on top of it to hold it down. Tomorrow evening I will put the car back together and get some results and report back. Fingers crossed!

 

hmm very interesting! thanks for sharing

 

Thank you for sharing this.

 

Following up after taking a drive. It works great! Still got the idle issue, but no more limp mode. Also, don't no if it's my imagination or not, but the throttle feels a bit more responsive too. Felt like I had a bit more power.

Overall it was a cheep and easy fix. Anyone with an out of wack afm should try this out before tossing it and find a new one.

 

Good, useful information. The measurements saved me from ugly trial-and-error that would have marred the duct.

 

i've described how to cure the idle issue before.

also the AFM does not cause any sort of limp mode, so i suspect that issue will also come back as temperatures get higher, since faulty OMPs at first usually show signs only on the hottest of days of going into limp mode.