can you use an "I" maf on an "E"?

[flyboyx]

I have an 87 e that doesn't run right. i switched out the icv(car is old style motronic 1.0), fuel pressure regulator, etc...

i don't have a spare "e" maf, so i replaced the original one with an "I" version. now, the car runs pretty darn good only if i disconnect the hose going to the icv. this got me thinking....i took the intake off and stuck a screwdriver in the air vane inlet to hold the "I" maf open a little bit. with this concoction, it runs great with the icv hose plugged in to the intake boot. it appears that the vane simply isn't opening up to allow the engine to idle. i decided to reinstall the "E" maf and it runs like shit and dies after 5 or 10 seconds unless i stab the throttle whether icv hose is connected or not.

this makes me assume my "E" maf is bad and the "I" maf is incompatible?

i have another "I" maf that i can try, but i doubt 2 of them are bad?

anyone have thoughts?

[paperplane94]

I have an 87 e that doesn't run right. i switched out the icv(car is old style motronic 1.0), fuel pressure regulator, etc...

i don't have a spare "e" maf, so i replaced the original one with an "I" version. now, the car runs pretty darn good only if i disconnect the hose going to the icv. this got me thinking....i took the intake off and stuck a screwdriver in the air vane inlet to hold the "I" maf open a little bit. with this concoction, it runs great with the icv hose plugged in to the intake boot. it appears that the vane simply isn't opening up to allow the engine to idle. i decided to reinstall the "E" maf and it runs like shit and dies after 5 or 10 seconds unless i stab the throttle whether icv hose is connected or not.

this makes me assume my "E" maf is bad and the "I" maf is incompatible?

i have another "I" maf that i can try, but i doubt 2 of them are bad?

anyone have thoughts?

leaning out the mix with more air

richening the mix with more fuel

You should use the AFM (maf's don't have a vane) that was made for the engine since it was calibrated for it. If the car doesn't idle well with the original AFM then check the idle adjustment screw on the bottom of the AFM. If the protective cap is still on the AFM idle adjust screw, then you do not need to mess with it.

The problem may lie somewhere else, possibly a vacuum leak or another problem that is changing the fuel mixture.

Info on adjusting the idle adjustment screw at the AFM:

http://forums.bimmerforums.com/forum/showpost.php?p=18364832&postcount=16

[flyboyx]

cool, thank you for taking the time to post that. it is very helpful. actually, it is indeed an afm. i just used the wrong terminology.

i have been around the engine looking for air leaks. the problem, oddly is that it will not idle unless there is an air leak. ie: i have to disconnect the icv hose to allow idle air into the engine. this this tells me that the afm isn't opening enough to allow air through it at idle. with the hose disconnected and allowing air to bypass the afm, it actually runs quite good but i know this isn't right. with the hose connected, i have to keep stabbing the throttle to keep it running and the engine runs really really rich. with the icv hose disconnected and bypassing air, the engine may still run a teeny bit rich but as i mentioned it does quite good. it can actually be driven this way and does very well.

i have definitely thought of the idea that there could be something else wrong with the engine, but for the life of me, i can't think of what it could be.

[jlevie]

An M20B25 AFM won't work properly with an M20B27 engine, and vice versa.

[Andy.B]

Have you tested the tps, temp sensor, temp switch, and function of the Icv, fuel pressure, etc, as per Bentley manual? You can waste lots of time running in circles by guessing/throwing parts at it. Since there are no specific test numbers for the AFM in the manual, it is worth it to take an hour with a volt meter and rule out everything else before you replace it.

I wasted tons of time trying to correct a high idle problem on my eta until a simple test led me to replace the temp switch. Two minutes later idle is perfect.

[Andy.B]

The afm doesn't "allow" air through. It just tells the ecu how much air is going through. If you have to introduce an air leak to get it to idle, it sounds like the idle control system is faulty somewhere.

Sent from my Galaxy Nexus

[nando]

A) It's not a MAF. :p

B) No.

maybe it's gummed up. a bit of carb cleaner should do the trick.

[Cyrix2k]

Is your intake boot 100% leak free? Mine would hardly run at all until I replaced it. If you want a known working boot & AFM for a good price, hit me up. I don't have an eta motor any more, but the boot is floating around my trunk and I think I still have the AFM in the garage. The boot only has maybe 3k miles on it, lol.

Also, I take it you're only running the car while it's cold? Is the cold start injector working?

[paperplane94]

It's obvious that he is running rich, right? If he has to introduce air into the mix then he is compensating for a rich condition.

I would check your Fuel pressure regulator first. Then you could test some of the above.

[Gregs///M]

The 325e afm has an output voltage that is exponential in nature.

The 325i afm has an ouput voltage that is linear in nature.

Therefore the two are not compatible with each other.

[Cyrix2k]

It's obvious that he is running rich, right? If he has to introduce air into the mix then he is compensating for a rich condition.

I would check your Fuel pressure regulator first. Then you could test some of the above.

he's not adding air, he's adding fuel. The AFM is a an air metering device used to determine fuel input. Pushing the barn door open means the computer thinks more air is entering the motor and it responds by injecting more fuel. However, the throttle body is what determines air input so the volume of air being pushed in remains the same. This means he is running lean... The other possibility is that the AFM is simply damaged. IIRC, the door actuates a potentiometer so that the computer can read a value. Pots work by having a wiper ride on a carbon track. The track has a known resistance and as the signal has to travel along more of the track, the resistance increase (resulting in a lower voltage reading) and vice versa. If the track is damaged where the wiper sits at during idle, the car will run like crap until it is revved up and the wiper sits on the good portion of the track.