Adjusting the AFM
01-25-2009, 07:36 PM
#1
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Adjusting the AFM
I've read posts of members doing this and wanted to share this info from DowneyOffroad and ask how those of you have done this handle Warning #4 on this adjustment procedure.
Also, I am confused on how to tell if your running rich or lean with EFI. I know a carb running rich causes black smoke, but don't know if EFI does this.
If no smoke, what do you look for?
MASS AIR SENSOR MODIFICATION*
* Tampering not legal,
should only be modified for racing use.
The following adjustment can be used to richen or lean the air/fuel mixture from the factory setting. This adjustment could be necessary when using a Big Bore Throttle Body or other EFI modifications. The mass air sensor (MAS) is found on top the air cleaner canister on 1985-95 Toyota vehicles. The sensor is an aluminum housing with black plastic lid. Cut the seal holding the black plastic lid in place. Gently pry the lid from the housing. To adjust, first mark the original location of the hold-down clamp on the gear wheel so you can return to stock setting if necessary. Loosen the clamp screw and rotate the gear wheel a few teeth as necessary. Clockwise leans the mixture, counter-clockwise richens the mixture. After adjustment, replace the top plastic lid (see Warnings below).
WARNING #1 - Use caution when cutting the top lid seal with a hobby knife so that plastic lid is not cut or damaged.
WARNING #2 - DO NOT let spring loaded gear wheel unwind, you will not be able to find stock setting/home base.
WARNING #3 - Ensure you establish a good seal when replacing top lid, moisture can destroy the sensor electronics.
WARNING #4 - DO NOT use an adhesive which creates a gas or fumes when drying, fumes will coat and destroy the sensor electronics – you’ve been warned!
* Tampering not legal,
should only be modified for racing use.
The following adjustment can be used to richen or lean the air/fuel mixture from the factory setting. This adjustment could be necessary when using a Big Bore Throttle Body or other EFI modifications. The mass air sensor (MAS) is found on top the air cleaner canister on 1985-95 Toyota vehicles. The sensor is an aluminum housing with black plastic lid. Cut the seal holding the black plastic lid in place. Gently pry the lid from the housing. To adjust, first mark the original location of the hold-down clamp on the gear wheel so you can return to stock setting if necessary. Loosen the clamp screw and rotate the gear wheel a few teeth as necessary. Clockwise leans the mixture, counter-clockwise richens the mixture. After adjustment, replace the top plastic lid (see Warnings below).
WARNING #1 - Use caution when cutting the top lid seal with a hobby knife so that plastic lid is not cut or damaged.
WARNING #2 - DO NOT let spring loaded gear wheel unwind, you will not be able to find stock setting/home base.
WARNING #3 - Ensure you establish a good seal when replacing top lid, moisture can destroy the sensor electronics.
WARNING #4 - DO NOT use an adhesive which creates a gas or fumes when drying, fumes will coat and destroy the sensor electronics – you’ve been warned!
If no smoke, what do you look for?
Last edited by Bako88; 01-25-2009 at 07:49 PM. Reason: Not enough info.
As for warning #4, Sensor safe Silicone sealant, AKA: RTV. 
01-26-2009, 11:04 AM
#3
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Basic RTV is acetic cure and NOT to be used. If it smells like vinegar, don't use it.
Otherwise, sensor-safe sealant should be fine.
As for rich/lean, EFI can do it too. The symptoms are mainly the same between the EFI and carb as well- stumbling, black smoke, crappy throttle response, misfiring, etc. If you adjust the AFM, keep in mind that the ECU will use the O2 sensor and will override your AFM settings during normal operations- you'll only see a significant change in mix at idle and at wide open throttle.
Otherwise, sensor-safe sealant should be fine.
As for rich/lean, EFI can do it too. The symptoms are mainly the same between the EFI and carb as well- stumbling, black smoke, crappy throttle response, misfiring, etc. If you adjust the AFM, keep in mind that the ECU will use the O2 sensor and will override your AFM settings during normal operations- you'll only see a significant change in mix at idle and at wide open throttle.
01-26-2009, 11:36 AM
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Emphasis on the "dont let the gear/spring unwind" bit. I let mine unwind a bit, but I got it back to a normal running state. Right now it's not too lean and not too rich, so it's as good as I could get it by sound and smell.
Wish there was a way to get it back to factory so I can sleep soundly at night.
Wish there was a way to get it back to factory so I can sleep soundly at night.
01-27-2009, 04:54 PM
#5
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You know, I'm not sure if adjusting the AFM really does anything. The ECU is a closed-loop system and it's going to see that the mixture has changed and compensate for it.
01-27-2009, 05:16 PM
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That's why I said that during normal operation, the ECU will use the O2 to compensate. You'd only see the effects of the adjustments when the ECU is 'open loop': at idle or wide-open-throttle. Arguably, two clicks one way or the other is within the range of compensation of the ECU when using the O2 as feedback but could help off-idle and full-throttle response. But if you go too far, after some driving around town and on the freeway/highway, the ECU may throw a code relating to too rich or too lean.
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02-04-2009, 05:50 PM
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my 78 and 81 Scirocco's had nothing similar at all. 
oh woe the days of k-jetronic: adjust the fuel distributor to a 50% duty cycle on the frequency valve and be done with it... weep, weep.
oh woe the days of k-jetronic: adjust the fuel distributor to a 50% duty cycle on the frequency valve and be done with it... weep, weep.
Last edited by abecedarian; 02-04-2009 at 05:51 PM.
07-06-2021, 01:00 PM
#10
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Closed loop?
Last edited by niQ; 07-06-2021 at 01:01 PM. Reason: Missed words
07-06-2021, 03:13 PM
#11
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this is affecting my rig generously. It has an egr delete and new motor and it will not run at the stock maf/AFM position at all. You run it up way rich and that’s the only way it’ll run. And then it surges in rpm’s up to 2 grand down to 1 grand over and over and over. Tell me why. I’m so irritated. Brand new motor and it won’t even run right. LcEngineering EGr delete kit. Also the idle screw on the throttle body? Hah. Does nothing. I’ve taken throttle body apart, cleaned the whole thing. Readjusted the tps. Please for the love of god tell me what I’m missing
07-06-2021, 03:23 PM
#12
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Honestly I traded my truck for this 4runner he put a brand new motor in it with new headers and exhaust all the way back precision injectors LCEngineering EGR Delete. This is my first ever Toyota. I cleaned the whole throttle body and put the tps on to where i thought it was when i took it off. i didnt know the idle screw had an oring cause i havent brought it out that far. all the vacuum lines that were taken off for the egr delete most of them were plugged/capped off i went around with carb cleaner and didnt hear much of a change in rpm's because of the surging when i richen it up or it dies when the AFM is in the stock position. honestly about to take it to a shop ive never had this much if a problem before
07-06-2021, 03:56 PM
#13
Honestly I traded my truck for this 4runner he put a brand new motor in it with new headers and exhaust all the way back precision injectors LCEngineering EGR Delete. This is my first ever Toyota. I cleaned the whole throttle body and put the tps on to where i thought it was when i took it off. i didnt know the idle screw had an oring cause i havent brought it out that far. all the vacuum lines that were taken off for the egr delete most of them were plugged/capped off i went around with carb cleaner and didnt hear much of a change in rpm's because of the surging when i richen it up or it dies when the AFM is in the stock position. honestly about to take it to a shop ive never had this much if a problem before
sounds like you may need to look into adjusting the TPS.
https://www.4crawler.com/4x4/CheapTr...PS/index.shtml
11-14-2021, 08:02 AM
#15
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it was a bad AFM, but I would like to tune this replacement one I have and I should see in to how to do that with the O2 sensor voltage. It also had a bad knock sensor, bad tps. It still surges idle very random at idle sometimes at a stop sign for like 2 seconds then it’ll go back to normal idle though. It’s runnin better than it ever has and doesn’t have a CEL so I haven’t messed with it.
04-24-2022, 12:07 AM
#16
04-24-2022, 05:11 PM
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I hope you realize that "tuning" the VAF doesn't do anything. I know that there are plenty on this site who will tell you that adjusting the VAF "only two clicks to the right" (or was it to the left?) made the sun shine brighter and the birds sing sweeter. But it just doesn't make any sense at all.
Nominally, the VAF tells the ECM that the engine is sucking "14 poohs" of air. The ECM looks it up in the table, and decides the engine needs "1 piglet" of gasoline, which it controls by setting the injector open-time. All done? Not so fast. How do we know your VAF is calibrated correctly? How do we know that setting the injector open-time to 1.2msec is "1 piglet" of gasoline? Just the temperature of the gasoline makes a difference! Add in wear and tear on the FPR, injectors, induction plumbing, etc. But the ECM knows! The O2 sensor (working in closed loop) tells the ECM that everything is running a tad rich. So the ECM backs off the gasoline just a tad. And to avoid doing this every few milliseconds, the ECM remembers this adjustment in the form of short term (and long term) fuel trim. All the calibration wrapped up into one adjustment.
So let's say you've heard you can turn your truck into a fire-breathing (and polluting) dragon if it just runs a little richer. So you set the VAF three clicks to the left. Then, when it's really sucking just 12 poohs, the VAF reports it's sucking 14 poohs of air. The ECM sets the gasoline to "one piglet," which is actually too rich for the 12 poohs of air the engine is actually sucking. Whoo Hoo! Enormous power (and clouds of black smoke)! Uh, no. Again, the O2 sensor is on the job, and finds that all these settings are making the engine run too rich. So the ECM resets the fuel trim to make it right. And all the fussing you did with the VAF was a waste of time.
Leave the VAF alone. If your engine is running rich, or lean, or else where, it won't be fixed by messing with the VAF.
Nominally, the VAF tells the ECM that the engine is sucking "14 poohs" of air. The ECM looks it up in the table, and decides the engine needs "1 piglet" of gasoline, which it controls by setting the injector open-time. All done? Not so fast. How do we know your VAF is calibrated correctly? How do we know that setting the injector open-time to 1.2msec is "1 piglet" of gasoline? Just the temperature of the gasoline makes a difference! Add in wear and tear on the FPR, injectors, induction plumbing, etc. But the ECM knows! The O2 sensor (working in closed loop) tells the ECM that everything is running a tad rich. So the ECM backs off the gasoline just a tad. And to avoid doing this every few milliseconds, the ECM remembers this adjustment in the form of short term (and long term) fuel trim. All the calibration wrapped up into one adjustment.
So let's say you've heard you can turn your truck into a fire-breathing (and polluting) dragon if it just runs a little richer. So you set the VAF three clicks to the left. Then, when it's really sucking just 12 poohs, the VAF reports it's sucking 14 poohs of air. The ECM sets the gasoline to "one piglet," which is actually too rich for the 12 poohs of air the engine is actually sucking. Whoo Hoo! Enormous power (and clouds of black smoke)! Uh, no. Again, the O2 sensor is on the job, and finds that all these settings are making the engine run too rich. So the ECM resets the fuel trim to make it right. And all the fussing you did with the VAF was a waste of time.
Leave the VAF alone. If your engine is running rich, or lean, or else where, it won't be fixed by messing with the VAF.
Last edited by scope103; 04-25-2022 at 12:34 AM.
04-24-2022, 06:03 PM
#19
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Reply
I hope you realize that "tuning" the VAF doesn't do anything. I know that there are plenty on this site who will tell you that adjusting the VAF "only two clicks to the right" (or was it to the left?) made the sun shine brighter and the birds sing sweeter. But it just doesn't make any sense at all.
Nominally, the VAF tells the ECM that the engine is sucking "14 poohs" of air. The ECM looks it up in the table, and decides the engine needs "1 piglet" of gasoline, which it controls by setting the injector open-time. All done? Not so fast. How do we know your VAF is calibrated correctly? How do we know that setting the injector open-time to 1.2msec is "1 piglet" of gasoline? Just the temperature of the gasoline makes a difference! Add in wear and tear on the FPR, injectors, induction plumbing, etc. But the ECM knows! The O2 sensor (working in closed loop) tells the ECM that everything is running a tad rich. So the ECM backs off the gasoline just a tad. And to avoid doing this every few milliseconds, the ECM remembers this adjustment in the form of short term (and long term) fuel trim. All the calibration wrapped up into one adjustment.
So let's say you're heard you can turn your truck into a fire-breathing (and polluting) dragon if it just runs a little richer. So you set the VAF three clicks to the left. Then, when it's really sucking just 12 poohs, the VAF reports it's sucking 14 poohs of air. The ECM sets the gasoline to "one piglet," which is actually too rich for the 12 poohs of air the engine is actually sucking. Whoo Hoo! Enormous power (and clouds of black smoke)! Uh, no. Again, the O2 sensor is on the job, and finds that all these settings are making the engine run too rich. So the ECM resets the fuel trim to make it right. And all the fussing you did with the VAF was a waste of time.
Leave the VAF alone. If your engine is running rich, or lean, or else where, it won't be fixed by messing with the VAF.
Nominally, the VAF tells the ECM that the engine is sucking "14 poohs" of air. The ECM looks it up in the table, and decides the engine needs "1 piglet" of gasoline, which it controls by setting the injector open-time. All done? Not so fast. How do we know your VAF is calibrated correctly? How do we know that setting the injector open-time to 1.2msec is "1 piglet" of gasoline? Just the temperature of the gasoline makes a difference! Add in wear and tear on the FPR, injectors, induction plumbing, etc. But the ECM knows! The O2 sensor (working in closed loop) tells the ECM that everything is running a tad rich. So the ECM backs off the gasoline just a tad. And to avoid doing this every few milliseconds, the ECM remembers this adjustment in the form of short term (and long term) fuel trim. All the calibration wrapped up into one adjustment.
So let's say you're heard you can turn your truck into a fire-breathing (and polluting) dragon if it just runs a little richer. So you set the VAF three clicks to the left. Then, when it's really sucking just 12 poohs, the VAF reports it's sucking 14 poohs of air. The ECM sets the gasoline to "one piglet," which is actually too rich for the 12 poohs of air the engine is actually sucking. Whoo Hoo! Enormous power (and clouds of black smoke)! Uh, no. Again, the O2 sensor is on the job, and finds that all these settings are making the engine run too rich. So the ECM resets the fuel trim to make it right. And all the fussing you did with the VAF was a waste of time.
Leave the VAF alone. If your engine is running rich, or lean, or else where, it won't be fixed by messing with the VAF.
so how do i fix this issue then
