DIY: BMW Air Flow Meter Testing

Video tutorial on how to testing and troubleshoot a BMW air flow meter which is the design of an early style mass air flow sensor. This is a Bosch Motronic system and is also found on other vehicles besides BMW such as Alfa Romeo, Volkswagen, Porsche, Mazda, etc. Similar procedures may be applied to other vehicle, but refer to OEM specifications to ensure the values are the same. I also did two types of testing on the potentiometer which were done by both the resistance and applying voltage to the circuit. I would recommend doing the voltage test vs the resistance because it is a much more reliable test. The resistance test will always show the mildest of contact issues and magnify the readings. A faulty air flow meter can cause issues with starting, idle, fuel economy, throttle hesitation, throttle flat spots, and emissions. This particular tutorial was done on a 1984 BMW 733i equipped with a 3.2L inline 6 cylinder M30.
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Air flow meter refurbishment: • DIY: BMW Air Flow Mete...
Pinout functions:
6 - ground
9 - input voltage from DME
7 - output voltage from DME
22 - temperature sensor
Tools/Supplies Needed:
-3/8" ratchet
-10mm socket
-standard/flat screwdriver
-razor knife
-multimeter
-9v battery
-9v battery plug
-2 small connectors
Procedure:
-first start by removing the rubber intake elbow going from the air box
-ensure that the car is up to full operating temperature
-disconnect the O2 sensor on the firewall
-start the vehicle, while running, push the door inside the air flow meter inwards
-if the vehicle's idle increases while smoothing out, the air flow meter does need to be cleaned or calibrated
-next remove the air flow meter complete from the vehicle
-allow it to cool down because it will hold the heat for a little while and this can affect the testing of the temperature sensor
-the multimeter will be required to check the resistance
-my probing pins #6 and #22, between the temperatures 15-30°C (59-86°F), the reading should be between 1450-3300ohms
-you can also use a heat gun or hair dryer to determine if the temperature sensor is functional
-if there is an issue with the temperature sensor, unfortunately there is no part which can be purchased to replace it, but you can replace it with another sensor from a different air flow meter assembly or purchase another used unit or a new unit
-next moving onto the potentiometer starting with the resistance test
-probing pins #6 and #7, use the multimeter on the resistance setting
-open and close the door to view the values either increase or decrease, if there is drops along the way, there is the possibility of either having a dirty contact or the contact has worn spots
-moving onto the next test using voltage to determine the quality of the potentiometer
-using a razor knife, cut the silicone around the plastic cap and remove it prying with a standard/flat screwdriver
-install the smooth connectors on the battery plug, then connect the 9v battery and plug onto pins #6 and #9
-using the multimeter on the voltage setting, put on the one test probe on the arm and the other on the ground or pin #6
-open and close to view the voltage increase or decrease and determine if there is any drops along the swipe of the potentiometer
-if there is any drops or extremely low voltage when the door is fully open, the swipe arm needs to be adjusted or have the contacts cleaned
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© 4DIYers 2013
All Rights Reserved
No part of this video or any of its contents may be reproduced, copied, modified or adapted, without the prior written consent of the author.

[@jarrodgleason748]

first you taught me to adjust valves. now you are helping me troubleshoot idle issues. sub'd

[@4DIYers]

Thank you so much for the support :) I'll have plenty more vintage BMW repair videos in the future too. Hoping to wrap up a few things with my E23 so it's ready for spring.

[@caribeturf]

using an oscilloscope is the proper way to check the flow meter you feed in a square wave and move the flap thru it travel you will clearly see an fluctuation. Great video

[@jnande6820]

+1 Christopher Olson. I have Miller MAF conversion on my e30 with M20b25 and it rocks. I also changed injectors to 4 little 16.5 pound hour injectors and throttle response & file are awesome!

[@deanthacker2839]

Very useful video on BMW air flow meter testing. It helped me troubleshoot a problem with my E30.

[@4DIYers]

Awesome to hear and thank you for the feedback :)

[@turboeeyore]

just tuned up my vam from my 88 thunderbird turbocoupe. thanks for the walkthrough

[@4DIYers]

Excellent to hear, didn't realize the T-bird used the same system. Haven't seen a turbo'd model for a very long time, rare car. Don't forget to subscribe :)

[@YarraMates]

Another great tutorial thank you. My E24 BMW is having a hard time starting when the engine is warm; I think AFM will be a good place to start troubleshooting.

[@4DIYers]

Glad to help out and thank you for the feedback. I also have a video on how to adjust the valves on an M30 which could possibly be causing a hard start as well kzbin.info/www/bejne/nITCkGl9hpaAhNE

[@mogdefender8520]

Check the fuel pressure regulator. A ruptured membrane in the regulator will flood the engine by pushing gas into the manifold through the vacuum line. Could also be your speed sensor.

[@HorizonsUnlimited]

I am amazed that its impossible to find manufacturer's specs for these units. For example, the temperature sensor on the input to these air flow meters. I have temperatures and corresponding resistances and they follow a pattern, but who knows if they are within spec.

[@ChrisDan94_]

I’ve taken my car to BMW and several shops and get a different answer each time. When I’m at a stop light, foot on the brake my RPM is revving up and down like crazy. Threw some fuel system/injector cleaner from Walmart into it during my last fill up and it didn’t do it for a week. Then during my next fill up it started doing it again. Every answer I’ve gotten was the following! 1) Fuel injectors 2) Carbon air filter 3) spark plugs 4) brake flush Each shop gave a different answer. It’s an 08’ 328i automatic. 102K miles.

[@martinparker6536]

idle control valve ?

[@HorizonsUnlimited]

I just tested an air flow meter Bosch PN 0 280 203 023 for a friend who owns a 1991 Porsche 964. I have a DC power supply, so I was able to set the voltage to +5.00V at pin 3 with respect to ground (0V) at pin 4. The best way to observe the action at pin 2, the signal to the computer, is by using an analog meter and observing how smoothly the needle sweeps from 0.25V to 4.60V (the specs in the Porsche shop manual). A digital meter isn't very good at observing a sweeping transition.

[@4DIYers]

Excellent info, thank you for sharing! I ended up buying an analog meter to test a hall effect sensor. Much more responsive than compared to a digital meter.

[@E30ShedSkid]

you think you could intercept the throttle position sensor and use/alter that signal to mimic the AFM signal and run that the ecu. and then mimic the built in AIT sensor to a set cold temperature? basically hack the AFM and delete it

[@halesdad7167]

Dude! Thanks for the video. I am going to try to scavenge the carbon track from a junkyard unit, flip it in and see if it works..

[@sparkeyjones6261]

Well? Did it work?

[@cridram]

Nice video man, I want to know why is the air flow upside down is better for clean or performance I don't know thanks

[@marijuspuslys4630]

Hello, thank you for your video :) It very helpful to understand how it works. But I have one question. My car is e34 m30b30. Then I start with the connect air flow meter and if I open more the sensors doors, nothings change. Im tested with tester and it has the oms. I cleaned evething and adjust the contacts. The cold start with conected meter almost impossible,misfire and bangs, I dont know how to say correctly in english, but then I start the air flow meter disconected its works and after that if I conencted back, the motor star. The engine doesnt work correctly and If I gave more gas, engine stall, but if I realeast and gave it more ir works not very corretly, but better. I try to drive the car, untile 2k rpm it goes not very bad not very well but with more gas its stall.If I disconected the sensor it works a little bit better. What should I do? where is the problem? Have I have to change Air flow meter or try to adjust that black wheel with the spring and should richer or less the mixture? P. s. one more thing. I saw a video that some arabic guy paint the track on the circleboar with carbon paint (if I heard correctly). And put back together and it works. What do you think of that? I wanna look for some resort, because in my country all meter cost about 70-100 euros and condition its like a lottery.

[@Dave-es2lp]

Great video I am in doubt what the result should or should not be while pushing the door inwards of the AFM with running engine. In the video i see it increases, is that what it shouldn't do? I also read that it shouldn't increase while smoothing out (?) Many thanks!:-)

[@4DIYers]

jeroen den Outer Thank you. If the idle increases and somewhat smoothens out, then it does need to cleaned/adjusted. What happens is the potentiometer get dirt or worn, on the area it normally rests at. This is turn causes some mixture issues.

[@carlosobeid2231]

Hello, thanks for this video, I have a 1985 528I bmw , I was having troubles when I start it at cold weather , a mechanical changed my idle to get it high for a faster turning on at winter ..but when I drive for about 15 minutes my idling become unstable and my car turn off when idling .. how can I fix it please? Thanks in advance

[@jacobepstein8527]

so per your initial test with your hand... when the car is fully warmed up, and you perform this test, if the AFM is good, the idle won't change? and if it's bad, it will increase/decrease? I'm testing mine now. If it slowly push the door inward, the idle increases. If I abruptly push the door all the way in, the idle decreases, and car the gets close to stalling

[@johnjeppsson17]

When I check resistance for the temperature sensor inside the unit I am not getting a consistent number and the number I get almost immediately goes away on my voltmeter. Does that mean the temperature sensor is bad? (Ambient room temperature about 70). Any idea where to purchase the replacement?

[@jebohim]

Have You managed the problem? In Bentley repair manual there are intake air sensor values, so when You have them You can buy thermistor and solder it

[@matreyia]

Would this cause an o2 sensor control fault code? I replacet my o2 sensors twice in a month just to be sure and that error keeps returning.

[@dokterkarel]

I have a question. With running engine you push in the flap so you fool the computer that there is more air intake. The idle changes, and you say that it needs to be recalibrated. Why is that? I mean: it SHOULD change the idle when you change the sensor's ohm's on purpose, right?

[@michaellovell3659]

My car (86 325es with 885 head) randomly loses power at wide open throttle and higher RPMs. The loss of power is abrupt and alarming, feels like a dog getting to the end of its leash. It's a real jolt. Could this be the issue?

[@SuperGlobalKiller]

I tested the temp sensor like you said on 6 different cars, same amf types, i get no readings whatsoever, bo sound when doibg the beep test, am i doing it wrong or are they all broken.

[@4DIYers]

Have you touched the probes together?

[@SuperGlobalKiller]

@@4DIYers the two outer probes yes, multimeter on ohm 2000, also sound test, seems like no connection in any of them. I do not understand, can’t imagine they are all broken. I’ll upload a video tomorrow where i do it live, you can judge if i’m doing it right. Thanks for answering!

[@alexsafari2933]

Drove my 635 CSI around the country, and, it ran great and shifted perfectly Stored it Airport Hanger and went away on my overseas assignment around Sept 2014 Now all of the sudden the car starts up and idles, however, does NOT rev up, and, when stepping on the gas pedal it bogs down and wont rev up Would you say this problem is due to a sensor malfunction such as the M.A.F or cold start valve? Would you consider receiving, inspecting and servicing our M.A.F.? Many Thanks in advance Col Alexander Klein

[@4DIYers]

+Alex Safari Could possibly be the air flow meter, you would have to follow the test in the view to determine if that's the issue. Also the door on the AFM may also be stuck. There may also be an intake issue such as a plugged air filter, or a fuel issue such as a plugged fuel filter. Other issues can also be faulty spark plugs, spark plug wires, distributor, idle control valve, or a vacuum leak. I do not offer a service to refurbish n AFM, but I do have a video on how to do it yourself which is a link in the video located at 3:00. I also have a video on how to test the throttle position sensor as well which is a link located at 4:00.

[@brianmbera3894]

hi, my e12 528i dies out after a slow run, or if on the high way can drive at high speed but when i slow down it dies out, when i drive at a constant speed its fine then if i push down the peddle, it dies out. when it dies out, i just give it a min or 2 having done nothing then it starts and goes runs again, any help?

[@bartekkarpowicz914]

Hi, I have question to resistance test with heating. in my both AMF which I own, resistance stopped at ca. 700 ohms. I own 1989 535 e34. Is that OK or it should run lower?

[@suwan1929]

Can this test be done with a afm from a m10 jetronic engine? Are the pins the in the same order? Pin 1and5 i get 396 at 29°C

[@benjaminuirableonard8250]

Awe

[@useribp]

If u let it open remuve the gate what can happen ?

[@4DIYers]

It won't work properly, the gate is what monitors the airflow. While it's still an AFM, it's technically a mechanical version of an MAF.

[@mgbrv8]

Will this procedure work on a 1987 325i

[@4DIYers]

Yes it should be, although I would double check on the clearance specs.

[@mclarkallen]

Great video. Lots of additional info at this link. Same meter is used on the VW buses and Porsche 914 and 912 with air cooled flat 4 engines.www.itinerant-air-cooled.com/viewtopic.php?t=7761

[@4DIYers]

Thank you and excellent info, thank you for sharing! Don't forget to subscribe :)

[@ErDuca21]

How can I clean it?

[@4DIYers]

I have a video for that, just check through my video list.

[@ahmadsoughar4918]

when i did the first test, my car stalled... i disconnected the o2 sensor and push the flap a little and it just turns off, does that mean that its working properly?

[@4DIYers]

Ahmad Soughar How far did you push the flap??? If you push it too far, it will change the mixture to drastically, therefore making the car stall.

[@ahmadsoughar4918]

it never stalled

[@joekochkarian8530]

hi there my name is joe, i have bmw 320i model 1987, i wanted to tell u about a severe problem in my car, i dont know if it is from the airflow meter, so its starts normally and runs normally but after running a certain millage it chokes and turns off, i am capable of restarting it after 15 to 20 minutes and rerun a certain millage and shuts off again, thank u

[@4DIYers]

Could be a variety of issues and is unfortunately hard to diagnose without seeing the car in person. It could possible be a fuel issue such as a failing pump. Once the car quits, can you hear the pump working? There could also be an issue with a relay or another electrical component.

[@joekochkarian8530]

Thanks for replying, in fact it was electrical, it was the ecu chip that was getting heated, i figured it out after replacing many electrical parts including the influmeter, the last thing i left to test was the ecu, so i ran a test on it by driving my car till it stopped and i replaced in 3 seconds the ecu and the car started from the first try, i also ran for to hours to make sure that i resolved, anyway thanks folks for the your tips, i hope u can publish my experience so other can get the benefit, thanks again, peace

[@christopherolson7656]

miller maf conversion. problem solved

[@cockasorrus7475]

Fantastic! Thank you!!!

[@4DIYers]

Thank you and happy to help :)