Bad afm symptoms

[Gklock15]

I have a 1985 318i and have been having idling issues and its not my icv and I don't thinks its vacuum because all hoses have been replaced I was wondering maybe afm but don't k ow symptoms of a bad one

[Gregs///M]

Common symptoms of failing AFM is as follows: (in no particular order)
-Weak or poor idle
-Feeling of under powered engine output
-Misfire type symptom. Brief and sudden loss of power but power instantly returns.

Basically, if you are not using a remanufactured or refurbished AFM, your AFM should be considered bad. I would not consider any 30 year old AFM to be anything other than bad.

[TobyB]

Of course, you could stick an ohmmeter (or the ohms function of a DVM) on it,
move the flap through its range of motion, and be sure.
It takes longer to find the meter and get the intake boot off than it does to test the AFM itself.

t

[Gregs///M]

Of course, you could stick an ohmmeter (or the ohms function of a DVM) on it,
move the flap through its range of motion, and be sure.
It takes longer to find the meter and get the intake boot off than it does to test the AFM itself.

t

This won't work. DVM's measure voltage and/or ohms by calculating an average. So if you did use this method to test your AFM, you'de only be looking at an average.

Voltage drop spikes or drops in impedance can happen in the millisecond scales as you rev your engine. Therefore, a DVM would never catch it. Only an oscilloscope or acquisition system would catch it.