This video provides some general information on how the air flow meter (AFM) on the Toyota 22RE EFI motor functions, as well as how the idle mixture / trim screw adjustment factors into the mix.
In very simple terms, when you turn the idle mixture adjustment screw on the AFM, you are tricking the ECU into thinking more or less air is entering the motor; the computer will respond by either slightly increasing or decreasing the target air fuel ratio - as described further below:
1. Turn screw clockwise (CW) = richer
2. Turn screw counter clockwise (CCW) = leaner
But why? When the screw is turned CW, it blocks off the secondary air bypass channel of the AFM. This results in more air pressing on the door inside the AFM and the AFM sends the ECU a voltage reading which indicates "more air" (i.e. the door is being pushed open slightly more) and thus the ECU responds by thinking "more air means we need more fuel" - it then slightly increases the pulse duration of the fuel injectors to supply more fuel.
When the screw is turned CCW, some air - which otherwise would have been pushing the door inside the AFM open further - can now bypass via the channel under the idle mixture screw; this reduces the pressure on the door inside the AFM. The ECU understand this new voltage signal from the AFM to mean "there is less air coming into the motor now" and it backs off the amount of fuel being added to match the perceived lower volume of air entering the motor.
In my experience, 2.5 turns CCW seems to be a fairly decent starting point, if you have lost the original factory adjustment. Alternatively, if your AFM housing still has the original number stamped on it, you can take that number (e.g. 26 or 30, etc.) and simply add 10.0 mm to obtain the original factory depth setting of the screw. For example, if the number you see is "30", then you would add 10 mm to arrive at 13.0 mm depth. A stamp showing "26" would represent 10 mm + "2.6" or 12.6 mm factory depth and so on ("28" would mean 12.8 mm). This depth measurement must be made accurately from the top edge of the screw hole housing down to the flat face of the screw itself - ideally using a digital or vernier depth caliper.
If you wish to gain a more comprehensive understanding of some of these areas, you may want to download the PDF version of the Toyota Computer Controlled System (TCCS) training manual here:
www.autonerdz....
The TCCS manual provides a lot of great information on what the ECU is doing in terms of controlling overall engine operation; much of the manual applies to the 22RE motors used in our trucks and vehicles, although the manual itself covers a wide range of Toyota EFI systems (not just the 22RE). The manual has specific information relating to the AFM and its factory idle mixture screw adjustment on pages 18 & 19.
PLEASE NOTE: While I do give some basic guidelines as to "resetting the idle mixture screw near the original factory position", final adjustments for your individual motor may vary and should be confirmed through monitoring of the VF voltage output levels via the ECU (see page 136 in the TCCS manual for more information on this).
Here is the AFM I'm running on my truck and shown in the video. I purchased it directly from Napa Auto Parts:
www.napaonline...
Негізгі бет Toyota 22RE AFM idle mixture screw adjustment / factory reset - how does it work & what is it doing?
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