air flow sensor......repair or rubish?

[pepe m42]

Hi!

problem is, i tested the air flow sensor
between pin 4 and 5 the resistance is ok.( so the little wire is ok)

between pin 1 and 2 while i move the little door the resistance is jumping up and down. totally not smooth ( i read in the manual it should increas smoot as i open the little door.)

The problem is if i stay on a high rpm (example:4500rpm) on the highway (traveling) affter a while it feels like i ran out of gass or like when you release the gass pedal and the step back on it, and in a second its gets back to normal. Also sometimes the power feels stronge then weaker, "(depens on i dont know what...)" In 1st, 2nd, 3rd...(in 4th and 5th i didnt try:)  i can rev the car, accelerate okay but its also feels different sometimes "(depens on i dont know what...)". but no signh of problems ... i think its because the rev just goes up until the tilt quickly, not like when im traveling on highway with an exact rpm.

is it possible to repair this thing or i need to buy a new Air flow sensor (it cost a lot, something like 5-600)
if i need to buy the oem then what is the different between them? what is rmfd mass or rmfd-vol...?
(AIR VOLUME DETERMINATOR WITHOUT CO-POTI
 RMFD MASS AIR FLOW SENSOR W/OUT CO POTI   
 RMFD-VOL. AIR FLOW SENSOR W ADAPTER LEAD)
http://www.realoem.com/bmw/showparts.do?model=AF91&mospid=47256&btnr=13_0307&hg=13&fg=15


i also read bmwman conversion thing but im not a big master of these things, so a basic explain could help.(thanks)
...could be its cheaper to get that conversion thing?


any help is thanks guys!

[Alpine003]

If it truly is your air flow sensor, I have a spare one I can sell you. But I'm not sure how costly it would be to ship it to you.

[silverblades181]

The M42 in the E30 used an Air Flow Meter (AFM) which is different from a Mass Air Flow (MAF). I know the M44 used a MAF, not sure about the M42 in the E36. You need to buy an AFM if you want to replace your unit...or do a conversion to a MAF which is costly but beneficial because the AFM is a big restriction to the air flow and not as precise as the MAF. The AFM uses a "barn door" to mesure the volume of air that enters using a potentiometer (like your Throttle position sensor or TPS) which is basicly a variable resistance. The computer sends a 5V reference signal and then reads how much is left after passing threw the AFM where the resistance varies depending on how open the door is which is relative to the amount of air coming in. The air has to physicly push the "barn door" and this creates a restriction that robs you of some power.

Newer engine will usually use a Mass Air Flow (MAF) which is a small heating element that is placed in a large conduit. Next to it is a thermistance, this is also a variable resistance but this one varies with the temperature rather then the movement of something. The air that comes in cools down the heating element and this system's job is basicly to keep the element at a given temperature. So the thermistance reads the temperature and when it drops, more current goes threw the element to raise it's temperature back up. The computer reads those variations and it can determine the mass of the air coming in, which is a much more valuable reading then just volume because, as we all know, there is more oxygen in cold air then in hot air. By measuring the mass, the computer has a more accurate idea of how much oxygen is in the air and can adjust it's fuel ignition accordingly.

Anyway, this is a very basic explanation of these two systems. You can't just plug a MAF instead of an AFM because the computer won't understand the readings. It requires more work. For your problem, I'd suggest getting a good used AFM, it's a lot cheaper then all the other options.

[bmwman91]

Yup, sounds like you got the same stumbling I did....it is only under part-throttle and not so much under medium to hard acceleration?  If so, and combined with your AFM test, sounds like you should get a new one.  Good luck!

[pepe m42]

THANKS for the info it was pretty clear!!!
Im iterested in that used AFM ... i sent a private message with some questions....