Tuning The Mixture By Adjusting The Airflow Meter

    The airflow meter is a device which measures the amount of air that is entering the engine.  This tells the computer how much fuel is needed for the best fuel mixture.  It does this by blocking off the airflow using a spring-loaded door which opens as you apply the throttle and air begins to rush into the engine.  The spring tension is very loose, this allows the door to fully open before you are at full throttle. The movement of the door creates a varying resistance across its range of motion much like a dimmer switch.  We can trick the computer into thinking that there is more air entering the engine by loosening the spring slightly that holds the door closed.  This is useful  if you have made changes to your car which allows more air to flow in and out of the engine, thus you also need more fuel to burn for maximum power.  The tools you will need for this project are an X-Acto knife or razor blade, A small flathead screwdriver, and some automotive silicone sealant.  I used the grey sealant from Permatex part number 599BR, this sealant meets Toyota specifications and is safe to use just about anywhere you need it. And some whiteout or white modeling paint.

    The first step is to remove the cover of your airflow meter.  On most cars it is the silver and black box that is just after the air filter.  Using the X-Acto knife or razor blade cut the seal around the black plastic covering like so.


    Once you have cut the seal all the way around use the small screwdriver to gently pry the cover off.  If you need to cut more of the seal.  It is ok to destroy the sealant as you will be putting new sealant in its place when you are done.  Just be careful not to destroy the plastic cover.   Once you are inside make a mark on the large black plastic gear inline with the screw next to it like so.


    The next step is a little tricky so take your time and be careful.  You will need to hold the gear in place while you gently pry outwards on the metal clip with the red arrow in the picture.  Remember the gear is spring-loaded so if you let go of it for even a second without the clip in place it will spin many times and be very hard to get back into place and might possibly ruin the AFM completely. To get a richer mixture you will need to rotate the gear in a counterclockwise direction.  Most people with basic intake and exhaust mods find that between 2 and 4 teeth work well.  Anything more than about 8 teeth will make the AFM function incorrectly, if you need this much adjustment it is time to buy a standalone programmable fuel injection computer.  If you have installed larger fuel injectors than stock and need to lean out the mixture some you can tune these in by rotating the gear in a clockwise direction.  Once you have reached your desired tuning point allow the spring clip to fall back into the valley of the gear teeth and breathe a sigh of relief that you didn't mess it up!  If you have an air fuel guage you can test your new setting to be sure it is what you want. 


Once you have things the way you want them you can peel off all the old sealant, reinstall the cover and apply a new bead of sealant around the edge.  For those of you who live in a smog nazi state you will need to purchase a second AFM to use when smog testing as breaking the seal on the AFM is considered tampering.


Created by Wesley Hetrick 3/27/2002