The afm flap issue again

[sierraspider]

My afm flap has been starting to stick more and more often often. I've taken off the outlet hose to plenum, reached in and it freed up easily, but it's starting to happen very frequently and the car won't idle or run worth shite. I read all the previous posts on the subject and I'm more confused. Note: I've had some historic backfires and I'm running a K&N oil type air filter. The flap itself looks pretty thick, so how exactly does it bend. What is the best way to test and service/clean it. Car was running very well before this problem cropped up.

Thanks

[vandor]

Does it have any play in it? Maybe the place where it pivots is wearing out.
I heard of ppl just sanding the chamber enough for the door to move freely, but it sounds like fixing the symptom and not the problem.

[sierraspider]

The flap moves freely, it gets to a point where is almost wide open and squeaks, then is sticky. Can they be cleaned without buggering up the electrical bits? It doesn't look bent or deformed. Upon closer inspection it has definitely been opened up by PO. I've run the car about 4k miles. Is there anyone out there that refurbs them other than buying a refurbed one ($280)

[76was124]

Two things can happen with the afm: 1. A sticking flap, 2 wear in the resistive feedback sensor trace under the black cover.

I would focus on #1, and not mess with the electronics(#2)

You can use carb or brake cleaner and spray the inside flap portion of the AFM, there are no electronics in air flow area. That may be all you need to do. If the flap is bent, it may still stick in spots after you clean it,. If it does, use a very fine sand paper (300,400 grit). And sand the housing were it sticks. There should be slight scrape marks where the flap hits the housing to help identify where to sand.

Technically, its easier to sand the sticking edge of the flap, but you wouldn't want to do too much of that. Don't be tempted to use course sand paper as you'll have small pieces of abrasive in the afm that could make it into the cylinders if you don't get it all cleaned out with carb or brake cleaner after your done sanding.

One other tip: I used a flat carpenters pencil and stapled sandpaper to it to make a long narrow sanding block. (staples on the non sanding surface of course, with short staples)

[bradartigue]

It bends because the backfire force is pretty extreme. Early AFMs had a solid door; late ones have a circular opening the middle of the door with a spring - when a backfire (a stuck open intake valve) occurs the little door opens and springs shut, saving the AFM flap. Oftentimes the little door with blow apart...it isn't a perfect solution.

All that said the flap bends because it is lightweight aluminum and is forced against the back of the AFM. Reinforced, thick, or not, a .05mm bend is enough to jam the flap.

[sierraspider]

Thanks for the responses. So what are the tolerances. I sanded the flap on the a housing and on the side scraping the housing. The is now just a bit more clearance than on the untouched side of the flap. Any guess at the effect. I haven't installed it yet.

Dan

[76was124]

I wouldn't worry about the amount of clearance as long as it moves freely with no sticking. Try holding the afm inverted, or rotated 90 degrees as well when you test the flap to see if it sticks. I know when I did mine, I had to do a little more sanding because it dragged a bit when in a different orientation.

I'm hoping you won't be driving your car inverted, as you wouldn't be too worried about your afm at that point!! However, testing the flap while inverted made me more confident that with temperature rise and possible expansion, or loading under high air flow, there would still be enough clearance vs. how it tests sitting on the bench at room temperature. Not sure that's true, but it appeared to have worked for me.

[RRoller123]

One thing I noticed is that there was a clear audible "chirping" sound that the flap made when it was rubbing on the housing. Sanding the housing slowly and carefully with 200-400 grit took care of the sticking and the chirp went away, as did the stumble and bucking.

[chrisfiat]

how about a couple drops of oil on the flap hinge pins too