AFM and Idle Issues (With Some Fuel Pump Issues Thrown In)

[bradartigue]

The flap opens at idle. The engine draws in air, the flap opens. The flap opens, the rod moves, the contact you see in your picture that the rod is resting on closes, and the fuel pump starts. If you have the key ON (but not the motor) and rotate the flap you should hear the fuel pump engage. If it does not then you've found at least one problem. If the flap doesn't move when you rotate the starter then you have a bad AFM (the flap is very stuck) or you don't have an air hose installed in between the AFM and the plenum.

Moving on, engine speed is not a function of the position of the AFM flap. The AFM flap is a metering device only. Rotate the flap by hand on a running engine and all you do is tell the ECU to dump more fuel, which the motor doesn't need, so you kill the engine.

Idle speed is set on the plenum with a screw letting air bypass the throttle plate and another screw setting the throttle plate position. Idle speed it set on an engine warmed to 190 degrees. If you can't get the engine to run then you have to figure that out before fine tuning idle.

[KevAndAndi]

One thing you said completely puzzles me, though: If "the flap should not open at all at idle" then how would the system energize the fuel pump (in the way it was designed to do)? I thought the opening of the flap closes the contact that energizes the fuel pump.

Looks like I shot off my mouth without thinking... You can see in this picture how little the flap opens/arm moves to close the fuel pump contact.

No problem. I get what you're saying now. Great pic; very helpful, thanks!

[KevAndAndi]

I think you could unplug the AFM and then turn the key on. If the pump does not run there is a good chance the AFM switch is internally bypassed. Often it only requires bending the arm of the switch under the black cover. If the fuel pump continues to run with the AFM unplugged the cars dual relay/fuel pump wiring has been messed with.

I will try that!

[KevAndAndi]

The flap opens at idle. The engine draws in air, the flap opens. The flap opens, the rod moves, the contact you see in your picture that the rod is resting on closes, and the fuel pump starts. If you have the key ON (but not the motor) and rotate the flap you should hear the fuel pump engage. If it does not then you've found at least one problem. If the flap doesn't move when you rotate the starter then you have a bad AFM (the flap is very stuck) or you don't have an air hose installed in between the AFM and the plenum.

Moving on, engine speed is not a function of the position of the AFM flap. The AFM flap is a metering device only. Rotate the flap by hand on a running engine and all you do is tell the ECU to dump more fuel, which the motor doesn't need, so you kill the engine.

Idle speed is set on the plenum with a screw letting air bypass the throttle plate and another screw setting the throttle plate position. Idle speed it set on an engine warmed to 190 degrees. If you can't get the engine to run then you have to figure that out before fine tuning idle.

My flap definitely does not open at idle, so the fuel pump is being energized either by (a) the closed AFM contact which is failing to be kept open by the rod, or (b) other PO wizardry. The car actually runs well, and I will do a full tune-up using your book at a later time. Eventually, I would like to be able to turn the key to the ACC position and not have the fuel pump run; I'd like for it to work as designed. In the meantime, the quick idle speed screw fix got me to a reasonable idle. I now need to figure out why the AFM flap is not opening (it only sticks slightly when I push it in almost fully). Examining the AFM may also give me a clue about the FP. I just have to crack that black box open...

[KevAndAndi]

I think you could unplug the AFM and then turn the key on. If the pump does not run there is a good chance the AFM switch is internally bypassed. Often it only requires bending the arm of the switch under the black cover. If the fuel pump continues to run with the AFM unplugged the cars dual relay/fuel pump wiring has been messed with.

I will try that!

Sure enough, with the AFM unplugged, the key turned to the ACC position does not start the fuel pump, so it would appear there is no PO workaround elsewhere energizing the pump. I also found that the clamp connecting the AFM to the air snorkel is defective and not providing an adequate seal. This would be air leak #2 (after the loose idle speed screw with its shrunken, hardened o-ring).

I'm going to remove the AFM so that I can tinker with it inside. My garage is too darn cold.

[bradartigue]

If the car runs then don't mess with the AFM. Put it back on. Get those air leaks sorted out first - they may be all that is wrong with it.

[lanciahf]

I agree with Brad, sort out the other issues before destroying the AFM.

[KevAndAndi]

If the car runs then don't mess with the AFM. Put it back on. Get those air leaks sorted out first - they may be all that is wrong with it.

Brad, I hear you and respect the opinion of an expert who literally wrote the book. I definitely intend to chase down any and all air leaks. But doesn't it make sense at this stage to also verify that the rod is in fact bent? It seems almost certain that it is, which surely qualifies as something wrong. I understand that I wouldn't want to straighten the rod yet, as that would de-energize the fuel pump which I would need to run the car and chase down air leaks. It's a chicken-and-egg thing. The AFM fuel pump contact rod needs to operate correctly, but in order for that to happen, the AFM flap needs to operate correctly, but in order for that to happen, the AFM fuel contact rod needs to operate incorrectly...

My reasons for wanting to mess with the AFM also included cleaning the interior, as it is dirty, and lubricating the flap hinge, as I understand those are common maintenance procedures, which along with chasing down air leaks should contribute to the objective of getting the flap working.

I certainly have no intention of unduly fiddling with or ruining the AFM!

If you still see a flaw in my logic, please let me know!

[bradartigue]

I'm lost, you said this car ran, which means the fuel pump works. Which means either the AFM works or someone made it work. In either case, if the thing is working and you know you have air leaks, fix the air leaks first. Get the idle set correctly (air leaks = high idle). You'll never diagnose the AFM with air leaks.

Certainly if the flap is stuck it is a problem that needs to be addressed (or the AFM replaced if you can't un-stuck it).

[courtenay]

Brad - I think the problem is that the fuel pump is coming on when the key is turned but before it gets to the run position. Given that it doesn't happen when the AFM is disconnected, it would appear that the rod in the AFM is bent.
I don't think, however, that the AFM needs to be taken out of the car to make this adjustment.

[KevAndAndi]

I'm lost, you said this car ran, which means the fuel pump works. Which means either the AFM works or someone made it work. In either case, if the thing is working and you know you have air leaks, fix the air leaks first. Get the idle set correctly (air leaks = high idle). You'll never diagnose the AFM with air leaks.

Certainly if the flap is stuck it is a problem that needs to be addressed (or the AFM replaced if you can't un-stuck it).

The fuel pump works, but I believe the only reason it does is that the rod in the AFM has been bent, causing the fuel pump contact in the AFM to be closed. (My idea was to confirm this by opening the cover.) That's the only way the contact can be closed because the AFM flap does not ever open. I ruled out creative wiring outside the AFM as being the reason for the fuel pump being energized, because when I unplugged the AFM, the fuel pump ceased to run. So, yes, the AFM "works," as it energizes the fuel pump but... it doesn't work, in the sense that the flap does not operate.

Correct me if I'm wrong: Chase down and fix air leaks, clean interior of AFM, lubricate door. These are all things that might get the door opening, right?

To be clear, the flap is not stuck. Rather it is slightly sticky when I push it all the way open with my finger. It does seem to be quite resistant to opening - not in a "sticky" manner but rather in a "spring tension" manner. In fact, to me it seems like far too much spring tension than could be overcome by flowing air, but perhaps I am underestimating the power of flowing air.

[KevAndAndi]

Brad - I think the problem is that the fuel pump is coming on when the key is turned but before it gets to the run position. Given that it doesn't happen when the AFM is disconnected, it would appear that the rod in the AFM is bent.
I don't think, however, that the AFM needs to be taken out of the car to make this adjustment.

Correct, on the first point. On the second point, you are also correct, but as my garage is cold, and my back hurts, I thought I would clean, lubricate, and inspect indoors on the workbench. If there's a real risk to removing the AFM, though, then I'll just man up and wear my insulated Dickie overalls!

[spider2081]

Going back to the original post I think Kevin stated 2 problems
Fuel pump running when the ignition switch is in the run position
Engine idle can not be properly set

It looks like the fuel pump running issue has been isolated to the AFM internal fuel switch.
It looks like the idle problem is more air leaks.

Sooner or later the switch needs to be inspected.
Removing the black plastic cover of the AFM is not too hard. Then the switch is exposed and its operation can be observed. Also the condition of the PC board in the meter can be seen. One problem I have seen with a couple AFM is the flap stop bends over time and the wiper on the PC board will run off the board. When the stop is bent the flap in the AFM has actually passed beyond closed and has opened in the opposite direction. Sort of like a swinging door. Could that act like an air leak?

I think its good practice to remove the air hose connecting the AFM to the throttle body and aux air vale. This hose then can be cleaned and inspected for cracks. I have seen more than one that crack in the ribs on the bottom. Flexing the hose off the car exposes the cracks. It is very common for the nipple for the aux air valve to crack where it mates the main part of hose. New replacements are very affordable.

[KevAndAndi]

Going back to the original post I think Kevin stated 2 problems
Fuel pump running when the ignition switch is in the run position
Engine idle can not be properly set

It looks like the fuel pump running issue has been isolated to the AFM internal fuel switch.
It looks like the idle problem is more air leaks.

Sooner or later the switch needs to be inspected.
Removing the black plastic cover of the AFM is not too hard. Then the switch is exposed and its operation can be observed. Also the condition of the PC board in the meter can be seen. One problem I have seen with a couple AFM is the flap stop bends over time and the wiper on the PC board will run off the board. When the stop is bent the flap in the AFM has actually passed beyond closed and has opened in the opposite direction. Sort of like a swinging door. Could that act like an air leak?

I think its good practice to remove the air hose connecting the AFM to the throttle body and aux air vale. This hose then can be cleaned and inspected for cracks. I have seen more than one that crack in the ribs on the bottom. Flexing the hose off the car exposes the cracks. It is very common for the nipple for the aux air valve to crack where it mates the main part of hose. New replacements are very affordable.

Thanks, excellent summation. The only thing I would add is that Brad's recommendation - to clean the idle speed screw and replace the o-ring if necessary (it was necessary) - was key. That alone got me down to a much more reasonable idle level. The second leak I found was where the air hose connects to the AFM. The worm gear on the hose clamp there is not grabbing. When I gently wiggle the AFM, it is clear that the connection is quite loose. Since I have to change that clamp, I might as well take off the air hose and visually inspect it.

What does everyone think about doing the propane leak-finding trick first?

Also, not to highjack my own thread, but what are everyone's thoughts about rubber air hoses versus aluminum? I like the "correct" look of the rubber, but there is something to be said for a material that is more resistant to cracks.

[courtenay]

I think you'll find a huge improvement when you get that air hose - afm connection sorted. I had the same problem some time ago and the car ran like crap! Once I got that clamp tightened up, it was a different car. BTW, getting the lid of the AFM shouldn't pose much of a problem. Mine just lifts off.