Do AFMs go bad?

[Erick]

Cliffnotes: Engine keeps shutting off when I downshift from 3rd to 2nd in fast driving. VERY bad throttle response in low rpms. Engine running rich. /me thinks it's the AFM.


Ok so here's the deal. I'm on the way home from Fedex on a spirited run through one of the handful of twisty roads in Florida. 3rd gear, coming into an S turn, heel and toe to 2nd gear and as I apply gas, I dont hear the revs.

I look at the tach and the revs keep dropping, at the point my heel is slamming the gas. Engine died. Feels like I flooded it. Weird.

Start up the car...... engine cranks, hesitates, dies. Try it again, gas all the way down, same. Try it again, and it cranks. Idle's funky, but it slowly levels out. I walk to the exhaust and I can smell the rich exhausts coming.... so rich I could get high off it.

So I get in the car after things seem back to normal and for shits and giggles I try it again. I take off in first and I have a VERY bad throttle response ( as in 2x or 3x worse than your average M20 AFM ) but past 2k rpms the power kicks in. 2nd gear through the turn...... 3rd gear turn..... coming into another 2nd gear, heel and toe again....... revs drop... gas gas gas..... engine dies.

Same "recouperating" process occurs. This time the CEL light came up. I turned off and did the punch the gas pedal 5 times to write down the code, but it didnt flash at all. When I took off ( driving smoothly all the way home )... I get a bad throttle response, even though I'm not pushing it.... and the Check Engine Light turns off the second you feel the power kick in from the throttle response lag.

The car drove home fine.... with a cranky throttle response that it always had ( nowhere near as bad when this was all happening, but worse than your average M20 ).

Any ideas? I think the AFM circuits are fried or something and that flap is not operating properly, because the engine goes to mega-rich when I crank the gas at low rpms. No vacuum leaks from anywhere in the intake system (my exhaust gaskets are bad)

Thanks,
Erick

[trent]

You wrote way to much. But to answer your question yes, AFM's are mechanical and do wear out. Look in the bentley and follow the procedure to check the resitance in the AFM.

[EtaSport]

could be afm, do you have anyone you could swtich with?

also when have you replaced plugs/wires/dist cap, rotor/and coil?
Sounds like a problem I had in my car. Replaced all ignition components and that fixed it.

[Erick]

You wrote way to much. But to answer your question yes, AFM's are mechanical and do wear out. Look in the bentley and follow the procedure to check the resitance in the AFM.

Hence the cliffnotes :)

I have the AFM from my parts car, and from the white e30 in storage. I'll check them out eventually, just too dark right now. I'll pull off the Bentley from the door pocket and give it a read.

As for your sig...... goddayum. 8)

[bichmgnt]

Check your O2 sensor as well. It could be telling your car that it is running too lean when it isn't.

Steve

[Erick]

Check your O2 sensor as well. It could be telling your car that it is running too lean when it isn't.

Steve

Doubtful, I replaced my O2 sensor not even a year ago. Nevertheless a possibility.

[rwh11385]

that's what happened when my M30 AFM went bad. I think the m20 electronics got fuckoreckedzzzz

[bichmgnt]

If you're running that rich for an extended period of time i think it can damage the O2 sensor. It's easy to check if you have a digital multimeter. With the ultra rich condition it should be reading at one of the extremes (1.0 VDC or 0 VDC) instead of bouncing around in the middle somewhere.

Steve

[Erick]

Here's my way to tell I'm running rich. I can smell the gas off my exhaust.

My friend kinda pwned his e30 today, so we were looking after it and I didnt get a chance to swap the AFM. Tomorrow though.

On a side note: I drove about 75 miles today and I wasted 1/2 of my gas tank.

[mspiegle]

just hook a volt meter up to that bitch and see what it does. Its the grey/yellow wire (signal).

At idle, it should be a steady voltage (probably higher than 0.75, but less than 1.5v). Then open the throttle a little and make sure the voltage goes up and down properly.

[mspiegle]

in fact, i take that back. Unbolt the AFM from the airbox, then put the voltmeter on it. Turn you car on, but don't start. Tinker with the barn door and make sure it goes from 0 to 5 volts.

[Erick]

I just went trial and error and changed the AFMs with my parts car. The throttle response has improved a lot, however it still seems like I am running a bit rich. I'm guessing that's because of something else now.

Thanks for the help though.
Erick

[Mike P.]

This sounds exactly like what was happening with mine when my AFM went south last year. I'm not sure where the tach gets it's signal from but the fact that you say you could see it fading down to zero vs. just slamming all the way down sort of tells me it's not ignition related. It very well could've been the AFM and now the O2 is possibly bad as a bad aftertaste.

Take it for what it's worth, but I'd almost put money on the AFM.

[Erick]

I swapped in the m30 AFM a couple of days ago when I last posted. I have had no problems since. Great improvement.

Tonight I am going to put some grip tires in the back and I will try the same situation again at the same place.... if it doesnt happen, I'm a happy man. :)