AFM failed / code 31

[enjoi.this]

My 1987 Turbo ran flawless last year before storage. When I fired up the supra after 4 months of sitting for winter storage it ran pretty well for about the first 5 minuets of running time. Burped the throttle a couple times then it began to idle around 400rpm and have an off idle heisitation/miss. Check engine light came on and it is a code 31, which is AFM signal. I followed the test procedure pre the pre-89 TSRM to check AFM and everything checked out fine through resistance and voltage tests.

Now the question is how often to AFM electronics fail? I noticed the little holes going to the inside the meter and am wondering if there could be something plugging them up inside. I have a K&N FIPK so maybe the oil from it could have done the damage?

 

[Kevin]

i believe you are not supposed to used oiled filters because they will "mess up" your afm..

do u know anyone with a good working one in ur area so u can quickly swap it and test it?

 

[WhtMa71]

Yea you're not supposed to use oiled filters but I have for 12k with no problems..and there's no telling how long the previous owner used it before I got it.

 

[TurboStreetCar]

The problem with the GTE AFM is it used a piece of reflective foil and a phototransistor. (maybe wrong component name) The foil moves in relation to air speed and the phototransistor creates a pulse signal (HZ) and that along with air temprature are calculated by the TCCS along with other data to come up with a mass airflow measurement.

If the foils reflective surface is compromised the AFM is effectively useless. Oil, Dirt or anything else could cause this at any time without warning. Mine dies overnight.

My car ran great one day tried to start it the next and it wouldnt barely run. Installed a MAFT GenII with a GM 3'MAF (basicly was the plan anyway) and i was good to go.

 

[enjoi.this]

Makes sense that your not supposed to use an oiled filter on it since the inside body of the AFM had a very light coating of filter oil on it. I ran mine for probly 10-12k before it shit the bed. Ill have to pick one up off someone on sm probly since there are almost no other mk3's in my area that arnt completely stripped of components. Thanks for the bit of info chunks, was curious on how it actually worked.