AFM is short for Air Flow Meter.

To make sure that the engine is running correctly, the ECU needs the input of several sensors. The AFM is one of those sensors.

In short, the AFM measures how much air is being sucked into the engine. This variable is needed to calculate the air/feal mixture. Pretty important data if you want your engine to run good!

The AFM is simply said a rather large metal 'flap' in a metal casing, attached to a variable resistor. A spring is used to close the flap (it's starting position).

The more air is drawn into the engine, the more the flap is forced open. This changes the resistance in the variable resistor, this makes a electrical signal that the ECU can use to calculate how much fuel is needed.

In the picture above, we can see that the AFM sits on top of the air filter housing.

Not every 4A-GE uses a AFM. It was mainly used on early 4A-GE's and in certain marketarea's.

Later 4A-GE's used a MAP sensor (Look at the article on MAP sensors for more info).

The biggest disadvantage of a AFM sensor is that it does form a restiction in the intake. This is one of the reasons why the AFM 4A-GE's make 'only' 115hp instead of the 125hp the later 4A-GE's make.

But it is said that the AFM sensor is more accurate than the MAP sensor.

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This part comes with a little help from ae92gts.com!

There is a little tric that you can do with the AFM from which is said that it would improve the throttlerespons.

I would like to point out first that the 4A-GE needs to rev to make good power. It doesn't have much power or torque in the lower rev ranges.

But this is also one of the reasons why people try to improve the power in the lower revband.

This may help. I haven't tried it myself yet (my engine isn't running yet) but I intend to try it to see if it makes any difference at all.

Like I said before. The AFM flap forms a restriction in the intake.

The thought behind this tric is that when you adjust the spring a bit so that the flap stays open just a little bit, This should give a bit better throttle respons because you fool the ECU into thinking that there is more air comming into the engine.

I still have my doubts, because I would think that the ECU would only inject more fuel, which would end up on the engine running a little rich. But who knows, it shouldn't hurt to try and if it doesn't work it can be restored to it's original position

The air might flow to the engine easier with this modification.

Ohw well, everybody should deside for themselfs what to do with this information. I'm going to try it and if it doesn't work, I'll just restore it to it's original position.

But please be carefull when atempting this mod, the AFM is a very expensive part!

What to do:

First you should remove the black plastic cover on top of the AFM. It is sealed in place, so use a sharp knife to remove it.

Now you'll see something like this:

Before you do anything else: Mark the current position of the clamp on the toothed gear. This way you can always restore it to it's original position.

When you've done that, you can loosen the clamp a bit and move it 2 or 3 teeth. You can experiment a little for the best setup. But it is said that you shouldn't go further than 5 teeth because you will loose drivability.

Don't forget to seal up the plastic cover again when you're done and make sure it's sealed correctly. You don't want any moisture in you expensive AFM!