a bad AFM acts like?

[325e '87]

When I'm accelerating my rpms rise unevenly. I'll get good power for a few rpm, then it stagnates briefly, then jumps again over and over until I finally need to shift. When the power is good it's great, it's the blips or pauses that irritate me.

I've got a new afm coming because I've eliminated almost everything it could be, fuel pressure, vacuum leak, dist cap and rotor.

[Mook613]

Yeah, that would a be a sign of a bad AFM.
There is an arm inside the AFM that sweeps along a carbon track. As the RPM build the arm will move.
Over time that carbon track wears away and is left with some low spots.
When the tip of the arm hits a worn away spot it no longer sends the correct signal to the ECU which results in the power loss.
As you pass through the worn spot it may reconnect to a less worn part and then you get power back.

New or refurbed AFM will have a clean track (or have the arm moved up to an unworn part of the track) and you will get a good consistent output as the ECU needs.

[325e '87]

Thanks. I've watched my afm in action thanks to a go pro. I've also ohm' d it out and there appear to be dead spots in the sweep. My low confidence remains because I haven't had the opportunity to test out a known good one, which I will receive via FedEx on Tuesday. I'm hoping I can put this gremlin to rest.

My strategy is:

1. New afm
2. New O2 sensor
3. New cps

All 3 will happen, but not all at once because I want to see the results from each change.

[badwella]

My strategy is:

1. New afm
2. New O2 sensor
3. New cps

All 3 will happen, but not all at once because I want to see the results from each change.

Good plan. I had a bad AFM track on mine. When I opened it up I found a severely worn spot right about where it would be at 3k rpm which coincided with where the cruise control would most likely be set for highway driving.

I would hit 3k rpm and it would stumble and then jump back to life. It got bad enough that when it would stumble it would backfire super loud as well. Moving the arms to fresh track and cleaning the whole unit made a big difference.

[325eMattyd]

i had a similar problem on my 87 325e, once i went over 3k it would break up until 4.5k, it ended up being the air flow meter,

[325e '87]

Thanks y'all. Now I've got my hopes up. I'm really looking forward to a smooth power band.

[Old525i]

Wasn't someone successful in replacing the AFM with a MAF?

[YosemiteSam]

Wasn't someone successful in replacing the AFM with a MAF?

Miller makes a kit, but it is not cheap. In order to replace your AFM with a MAF you have to chip the ECU with a chip designed for a MAF. The signal out of an AFM is fundamentally different from the signal out of a MAF, so if you just hook up a MAF a stock ECU will have no idea what's going on.