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AE112R / 7A-FE intermittent idle surging, fault code 31


LP76

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ok fair enough so its not an ECU signal stopping it from getting into closed loop then....
OK u are the ONLY person i have found that sais they fixed a hunt by bleeding the cooling system, haha, however I now understand what you're saying and can see that happening.
So this "auxiliary air valve" system is basically a cold idle increase thing. Sorry ive never dealt with one before.

I did read and saw people mentioning the "air in the coolant passage in the throttle body" in the topic but didn't associate the throttle body with any sensor so i just wrote it off. Now it makes sense, its not air in the throttle body coolant, thats Chinese whispers.

The issue i see is still that i can't see how it could HUNT.
the wax pellet has heat capacity, it doesnt immediately loose its heat when an air bubble is around it. If you do the thermostat in the boiling water test, you notice when u pull it out it takes a while to close.

The wax element in this auxiliary bypass valve would be the same. I can see it would make the idle slightly different depending on how much air is in the system, but i can't see how it would instantly open and close whit coolant touching and not touching repeatedly.
Maybe i ought to go pick up one of these valves in town from a surplus store (wrecker) and to some tests, as you say you managed to stop a hunting surging idle by getting rid of the air.

Sorry I'm not just putting up a fight, it just densest make sense.

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also i can see that as quite a dangerous system, anything that relies on secondary mechanics to keep the engine rpm under control is pretty dangerous.
2 reasons.

Cold driving may result in lack of engine braking, and

cold driving may result in brake booster functioning below capacity.

Do many people just bypass this thing all together?
I can see it would be quite high up in the system and would be difficult to bleed.

Edited by rebuilder86
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The older systems use the wax-pellet valve (or a bi-metallic strip), newer ones went to a thermoswitch sender and a rotary valve.  The newer valves also control all the idle-up functions too so can adjust for air-con, power-steering, electrical loads etc etc, they also don't tend to have an idle adjustment screw (unlike the old "dumb" systems).  They get called different things depending on the engine (cold-idle valve, aux air valve, idle-speed control valve etc) but they all do the same job - open up an additional passage through the throttle to let extra air in to the engine when the throttle blade is shut.

 

Another thing is that maybe we have different definitions of "hunting" or "surging" idle speeds.  To me, any idle speed that doesn't stay stabilise is "hunting", even if it stays at a particular rpm for several seconds.

Edited by Hiro Protagonist
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yeh I'm starting to think that its our definitions. for me, surging and hunting are the same thing, (only because ive never experienced the slower variety) but maybe surging should be reserved for rapid up and down like an ecu does via iac , and "hunting" maybe should be reserved for slow changes in base idle.

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On 20 December 2017 at 1:12 PM, Hiro Protagonist said:

The easiest way to determine if it is an idle-valve issue and not a vacuum leak is to take the intake pipe off to expose the throttle body, and then stick your finger over the hole for the bypass whilst the engine is warm and idling.  If the idle stops surging then the issue is in the ISCV (and either a faulty valve, sensor or air bubble), if it continues then the issue is a vacuum leak downstream of the throttle (or with the MAP sensor or TPS).

So, literally just close in the hole in the bottom of the throttle body (the one that leads to the ICV) when it's running? Problem is, every time i go to solve this fucking problem, the idle is fine!

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On 17 December 2017 at 10:26 PM, Hiro Protagonist said:

Trust me, anyone who has ever owned a 4AGE will have experienced the air-bubble in the T/B at some stage causing a hunting idle speed.

Gas is a poorer conductor of heat (convection) than liquid (conduction) too, remember.

Hi again.

So, I ran the car from cold to hot, and then for an extra 10-15 minutes, with the rad cap off AND the heater on (which I forgot to do last time).

Numerous bubbles came out when the motor became warm, and then finally stopped after several minutes. Could this have been the cause of the intermittent idle surging? I might re-iterate that the surging is not always present, and starts and stops with no apparent rhyme or reason. 

More annoying to me is the dead spot at the very beginning of the throttle. It is small, but definitely present. Surely it is should not be there?

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4 hours ago, LP76 said:

Hi again.

So, I ran the car from cold to hot, and then for an extra 10-15 minutes, with the rad cap off AND the heater on (which I forgot to do last time).

Numerous bubbles came out when the motor became warm, and then finally stopped after several minutes. Could this have been the cause of the intermittent idle surging? I might re-iterate that the surging is not always present, and starts and stops with no apparent rhyme or reason. 

More annoying to me is the dead spot at the very beginning of the throttle. It is small, but definitely present. Surely it is should not be there?

If it goes away for good, then yes it was most likely the cause :P  If not, them time to keep ticking things off the list.

 

I do notice a little flat-spot just off idle in my 7A, the old shell was worse though and could possibly be a stretched throttle cable, check to see if the butterfly moves straight away when you press the pedal or if there is a slight delay from a loose cable (you do need _some_ slack there, but not much).

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3 hours ago, Hiro Protagonist said:

If it goes away for good, then yes it was most likely the cause :P  If not, them time to keep ticking things off the list.

 

I do notice a little flat-spot just off idle in my 7A, the old shell was worse though and could possibly be a stretched throttle cable, check to see if the butterfly moves straight away when you press the pedal or if there is a slight delay from a loose cable (you do need _some_ slack there, but not much).

Okay will check the cable tomorrow. 

The idle surge has not been as frequent as of late, though one thing that has happened quite a few times is that when the motor is warming up, just after starting driving, it has almost stalled (and today it actually did stall) when coming up to a set of red lights. I notice it coming back down through the gears, going into neutral when finally coming to a stop. The revs drop almost to stalling speed (as I said, today it stalled once) and then surge back up before finally smoothing out. This has happened three times I think, and each time it has been after the car has been driven, stopped for a few hours, then driven again. Once it's warmed up to full operating temp it doesn't happen. It's very strange.

I'm starting to think I should maybe just sell it and get something else, as I'm pretty over it. Aside from this ongoing problem, the car is great, but the problem irritates me enough that a lot fo the time I wish I had something else.  

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do not give up.

can u explain what the old surging was like? how long would a single up and down surge last, ie would it cycle between high and low about once a second, or was it relitively long like a few seconds up high, then a few seconds down low?

i can feel ur frustration, but wed all really like to see u get it sorted.

the stalling while coming up to lights sounds like a fuel supply issue, either too much (way too much) or just not enough. here is one particularly common cause of stalling while cold after deceleration with EFI.

while relitively cold, the engine needs more fuel to combat the poor atomization, especially at idle. so before the engines computer switches over to leaned out closed loop mode with readings from O2 sensor, the only things which has a physical impact on fuel flow is the pressure regulator (vacuum vs spring strength). seeings as tho this is happening only before it gets hot, id again be suspicious of a vacuum leak on the actual hose to the fuel pressure regulator. (causing an extremely excesively rich mixture just after deceleration to idle).

The other potential problem could be that the regulators spring is becoming weak, making the suction signal have more effect on the FPR valve and potentially opening up the return line too much leaning out the mix and stalling out. This could be overcome by the hot engine as the fuel atomises better and the idle doesnt need as much fuel like that. So when cold it is so problematic it cannot run. when u restart the motor, the spring goes from completely relaxed (highest fuel pressure) to a nice mid level and doesnt become an issue again until a deceleration event occurs, including, simply revving the motor ans coming off the throttle abrubtly.

the electronic parts which may influence the fuel supply are the injectors and TPS and temp sender. but all of these can probably be ruled out because the issue goes away when they become more prominent in closed loop, whixh u would expect to see more problems from vacuum leaks and sensor faults.

 

i hope this makes sense

Edited by rebuilder86
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6 hours ago, rebuilder86 said:

do not give up.

can u explain what the old surging was like? how long would a single up and down surge last, ie would it cycle between high and low about once a second, or was it relitively long like a few seconds up high, then a few seconds down low?

i can feel ur frustration, but wed all really like to see u get it sorted.

the stalling while coming up to lights sounds like a fuel supply issue, either too much (way too much) or just not enough. here is one particularly common cause of stalling while cold after deceleration with EFI.

while relitively cold, the engine needs more fuel to combat the poor atomization, especially at idle. so before the engines computer switches over to leaned out closed loop mode with readings from O2 sensor, the only things which has a physical impact on fuel flow is the pressure regulator (vacuum vs spring strength). seeings as tho this is happening only before it gets hot, id again be suspicious of a vacuum leak on the actual hose to the fuel pressure regulator. (causing an extremely excesively rich mixture just after deceleration to idle).

The other potential problem could be that the regulators spring is becoming weak, making the suction signal have more effect on the FPR valve and potentially opening up the return line too much leaning out the mix and stalling out. This could be overcome by the hot engine as the fuel atomises better and the idle doesnt need as much fuel like that. So when cold it is so problematic it cannot run. when u restart the motor, the spring goes from completely relaxed (highest fuel pressure) to a nice mid level and doesnt become an issue again until a deceleration event occurs, including, simply revving the motor ans coming off the throttle abrubtly.

the electronic parts which may influence the fuel supply are the injectors and TPS and temp sender. but all of these can probably be ruled out because the issue goes away when they become more prominent in closed loop, whixh u would expect to see more problems from vacuum leaks and sensor faults.

 

i hope this makes sense

Ok I totally understand what you are saying. 

The surging is/was fairly slow; dropping down to around 400-500 over a second or two, then surges up to around 1100 over the same amount of time, then repeat, repeat...

I checked the vacuum hose going from the the manifold to the fuel pressure regulator. Seems okay, no cracking present. I also checked the hose from the regulator downwards as far as I could without getting under the car/really clambering around to follow where it goes.

I bled the coolant again with the rad cap off, and no bubbles came out.

I also made sure a code hadn't been thrown after the stalling event, and of course there isn't one present.

I dunno, I'm ready to give up. If it was a consistent thing it would be much easier to diagnose and fix, but because it so inconsistent, it seems like there is no way of trying to eliminate the potential problem through trial and error. 

 

 

 

Edited by LP76
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mm i understand that frustration. 

that sort of surging every 2-3 seconds is often a result of an IAC valve doing its thing with a faulty senaor, so the closeat equivalent of that in this car, like everyone else is saying, is this auxiliary air valve, controlled by the collant...

are u able to just temporarily bypass the throttlebody by putting a simple brass nipple between the coolant in and outs to simulate a cold engine? this would allow u to finally rule out or in this as the problem. that seems like the best analysis methid at this point.

 

there is also an idle speed screw on this thing i believe, at the top i believe, which if not adjusted propperly, is effectively a vacuum leak that u canr see or hear or test for.

Edited by rebuilder86
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7 hours ago, rebuilder86 said:

mm i understand that frustration. 

that sort of surging every 2-3 seconds is often a result of an IAC valve doing its thing with a faulty senaor, so the closeat equivalent of that in this car, like everyone else is saying, is this auxiliary air valve, controlled by the collant...

are u able to just temporarily bypass the throttlebody by putting a simple brass nipple between the coolant in and outs to simulate a cold engine? this would allow u to finally rule out or in this as the problem. that seems like the best analysis methid at this point.

 

there is also an idle speed screw on this thing i believe, at the top i believe, which if not adjusted propperly, is effectively a vacuum leak that u canr see or hear or test for.

I assume you mean bypassing the IAC valve by linking the two coolant lines together, yes? Won't that make the car just idle at around 1100rpm (which it does upon cold starting)? 

Also, I thought messing with an idle speed screw was generally frowned upon with an EFI motor? In any case, I noticed yesterday that there is a screw/bolt that appears to set the resting position of the throttle arm. Is this the screw you are referring to? When the car is idling well, and not surging, it stays around 750-800 rpm. This is a correct idle speed, surely? I increase the resting position of the throttle arm, that'll just make it idle higher won't it? Seems like an easy way to mask a problem, but creates another one by making the idle too high. 

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yes its frowned upon, and perhaps this is exactly why, perhaps it has been....., messed with??
I was suggesting that it may have been set too high, not a major suggestion, but one to consider.
Anyway, yes i was saying to bypass the throttle coolant passages. it will make it idle high yes, and if it does, and stays at a steady high idle, then u can confirm that it is the Auxiliary air valve which is causing the hunting.

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