Pulsating Idle, AFM Adjustment?

[joelittel]

My '80FI has a pulsating idle, meaning it slowly climbs 200 rpms then drops back down... over a second or so it slowly climbs back up 200 rpms (give or take) and then drops back down. Is this normal?

I've read about the contact points on the little arm (red arrow) making a connection with the clean part of the track and was wondering if mine could benefit from an adjustment.

I have what look to be two grooves (blue arrow) the entire length of the track, and thought it seemed logical that this could be the beginning of a problem.

Am I correct in thinking I can loosen the screw (yellow arrow) and adjust where the contact points on the little arm (red arrow) make contact with the black saw blade shaped track (blue arrow)?

[76was124]

Nice picture...looks like you did the hard part disassembling. There a few good posts in the forums. This one has a link by rlux4 that points to http://the944.com/afm.htm
Original post at: http://fiatspider.com/f08/viewtopic.php ... om/afm.htm

[bradartigue]

I'd go on a hunt for a small air leak before I'd mess with the AFM.

[narfire]

I've read about the contact points on the little arm (red arrow) making a connection with the clean part of the track and was wondering if mine could benefit from an adjustment.

Kinda -sorta. The screw/nut to loosen is actually just below your yellow arrow. it will allow the assembly to slide up/down on the shaft. Might have to give the pin arm just the slightest bend to get the pins to a clean part of the track. I found hardly a MM made a difference.
The moving of the pins to a cleaner part of the track will/could provide smoother running as the car accelerates.
What I hear you describe is while at idle the engine is surging a bit. My initial guess is you have an air leak somewhere. Non metered air is getting in after the AFM. Check all the vacuum connections inc. the one for the dist. How are the brakes? Any hissing sound when they are applied? Might be a pooched diaphragm. Some will use carb cleaner and gently spray the stuff around any of the usual suspects where air could get in.
Chris

[aj81spider]

I'm with Brad. I had a problem where my FI 1981 would lose power then surge back to full power - but only after I'd been driving for a half hour or so, and without any pattern. It turned out that the large hose between the AFM and the manifold had a crack in it. Replaced it and everything was fine.

[joelittel]

I have a compu-tronix distributorless ignition so no vacuum connection to the distributor to worry about.

My other hoses look terrible and I plan to replace them soon. See pic below.



Are there any others I should be looking at?

When I start the car, after it has been sitting long enough to cool down entirely, the surging is most noticeable. The car starts every time but it start with the rpms way down in the 300 range and "surges" it's way up to 1100 or 1200 rpms by the time it's fully warmed up. I've never been able to get it to idle below 1000.

I will clean the needle valve, O ring and orifice per Brad's guide.

I took the auxiliary air valve off and could not see any opening internally, it's closed up with no signs of a hole. The air temp in the garage at the time was 20 degrees F, so it's my understanding that at that temp I should be able to see through a small hole. I reread Brad's guide this evening and will go through the steps to properly set idle once everything has been cleaned and or renewed.

The hose before and after the aux air valve has been replaced.

The brakes have always felt a little soft, but there are no hissing sounds that I am aware of. The brake booster does not look like the easiest thing to pull out and check, is there an easy way to do this?

I will continue looking for air leaks before I adjust anything on the AFM. I was hoping to find a obvious problem when I opened it up, but I am very reluctant to "adjust" it myself.

[rlux4]

It is a good idea to check for vacuum leaks but a more probable source would be an intake air leak. Between the AFM and intake plenum. Check that the large boot is secure and has no cracks or holes in it. It's not necessary to have it tightened up to the extreme, I leave mine snug but loose enough to blow off in case of a back fire through the intake. You should have a small hole in the AAR at 20°. Even fully open though, it's not a large hole, maybe slightly smaller than a pencil. Put it in the fridge and see if it opens. You can clean it and spray a silicone lube in it to try to refurb it before you spring for a relplacement.
Ron

[narfire]

I have a compu-tronix distributorless ignition so no vacuum connection to the distributor to worry about.

What did you use to block off the port on the side of the intake?
I was going to change to one of Mark's ignitions when $$ permit.

[joelittel]

I used a cap and clamp, a silicone cap made for this application.

But now that you've mentioned it, I do not recall seeing iton the car last night.

[narfire]

[bradartigue]

I have a compu-tronix distributorless ignition so no vacuum connection to the distributor to worry about.

So we'll assume the distributor vacuum port on the plenum has been capped.

My other hoses look terrible and I plan to replace them soon. See pic below.

Easier path - cap them off at the air box for testing.

Are there any others I should be looking at?

A 200 rpm pulse will be from a rather small leak, like a disconnected 5mm line, or air leaking around the idle adjustment screws.

When I start the car, after it has been sitting long enough to cool down entirely, the surging is most noticeable. The car starts every time but it start with the rpms way down in the 300 range and "surges" it's way up to 1100 or 1200 rpms by the time it's fully warmed up. I've never been able to get it to idle below 1000.

Has air leak written all over it. Car heats up, hoses get hot, and the air leak gets smaller. Classic failure mode of an AAR or a leaking hose.

I will clean the needle valve, O ring and orifice per Brad's guide.

This has repaired many many many FI cars (the cleaning of the valve, replacing the o-ring, and resetting to spec).

I took the auxiliary air valve off and could not see any opening internally, it's closed up with no signs of a hole. The air temp in the garage at the time was 20 degrees F, so it's my understanding that at that temp I should be able to see through a small hole. I reread Brad's guide this evening and will go through the steps to properly set idle once everything has been cleaned and or renewed. The hose before and after the aux air valve has been replaced.

It is not your AAR if the AAR is stuck shut. If it is stuck open or is generally sticky then it may very well be this device. Plug the line to test.

The brakes have always felt a little soft, but there are no hissing sounds that I am aware of. The brake booster does not look like the easiest thing to pull out and check, is there an easy way to do this?

FIAT brakes are soft when boosted. Sounds like they are working right.

I will continue looking for air leaks before I adjust anything on the AFM. I was hoping to find a obvious problem when I opened it up, but I am very reluctant to "adjust" it myself.

It isn't your AFM. Well, that's my opinion. Do this, take the little black cap off and start the car. If the needle moves when the RPMs go up and down then the AFM is fine, because the flap is moving slightly due to your air leak, wherever it is. If the needle is dead steady, which I doubt it will be, and your RPMs are wavering, then yeah it might be your AFM. but you still have to go through and figure out if you have an air leak.

[joelittel]

I really appreciate all the help. You've given me a lot to go on, thank you.

I'll keep investigating.

[joelittel]

I've decided to try and clean out the auxiliary air valve before I spring for a new one.

What have you guys used to clean yours?

[narfire]

I sprayed brake cleaner in mine. Lots of black came out when drained.

[joelittel]

Tried cleaning mine with carb cleaner but no signs of improvement yet.

It's definately not air/water tight, should it be?