MAF - adjustment? How? Have new MAF but unsure how to adjust

[cirrusblue]

Hello R3v'ers,

I've been rejuvinating the intake and exhaust portions of my e30 street car and I got a new MAF. The one in there was original, and felt like cleaning it out, and replacing it and learning about the MAF's. Worst case I'll have backup.

There is a screw or adjustment key on the top right covered with a plug. The one on my original MAF was removed, I assume for adjustment.

How do you calibrate this? i think it has something to do with the mixture, but unsure how to know what to set it to. Any advice? Have anyone adjusted the MAF screw?

Thank you

- CB

[cirrusblue]

PIC

[cirrusblue]

"An adjustable bypass diverts a small quantity of air past the air-flow sensor flap. Variations in this bypass air quantity, which is independent of the sensor-flap position, are applied as the basis for correction of the air-fuel mixture for idle adjustment."

good article on maf

http://www.iprimus.ca/~trauttf/temp/AFM/

[jlevie]

That adjustment screw is as cirrusblue pointed out is to provide bypass air at idle. There is an adjustment procedure for it requiring an exhaust gas analyzer to set a specific CO level in the exhaust at idle.

The adjustment was set at the factory and should not be messed with.

[cirrusblue]

oh, ok. thanks Jim. Thing is, the MAF I have came in a box as a refurbished unit, so I didn't trust how that was set up for my car. Maybe I'll just wait on it, I don't have a way to check the exhaust gas for the proper o2...

[jlevie]

There is a flow bench procedure for setting the idle bypass and for testing the AFM. I would hope that whoever did the refurb either left the screw alone or properly set it.

If you have idle speed problems after installing the new AFM there are a number of other possibilities to investigate and or fix first.

[TobyB]

That said, it's how you set the idle air bypass volume, and within a certain window, the
IAC motor balances it out.

Outside of that window, the car either idles too high, or stalls, or hunts, or throws a CEL.

On other flapper door systems, I have dicked with that (when the IAC acted up) and
it CAN be used to crudely replace the idle air system. It's just not the RIGHT way to do it.

t

[nando]

A) it's not a MAF.

B) Don't fuck with it.

[rommeldawg]

well i am interested in the co adjustment to refine the idle a bit on an e30 i have recently come into. it appears the ecu was from a 535i (179) so i replaced it with a 380 from another 325i with same yr and trans as this one. power seems better with 380 and when engine is coming into or at temp car runs perfectly but cold start is little funky. looks like someone has been into the afm before as the plug has been replaced with a plastic one.

[jlevie]

I can't remember where I ran across the procedure for adjusting the bypass air. But before doing that you have to make sure that all of the engine management system is operating properly.

[rommeldawg]

i havent put on a scanner to check fuel trims when its cold and get other input but i am not getting a cel and i can gas it up a bit to compensate when cold. the 179 ran better cold but i swear the 380 runs better at temp... maybe i am imagining it i dont know

[nando]

Later E30s do not have an adjustment. That plug is likely stock.

[TobyB]

All the afm's I've looked at have the adjustment- many have a plug over the HOLE
to prevent you from 'fixing' it...

heh

t