4AGZE idle hunt problems

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4AGZE idle hunt problems

Postby GZE_RA21 » Sat Feb 27, 2016 11:36 am

Hey club4ag!

I've been on here for awhile but this is my first post, i looked here and on other sites for an answer but can't find many people who actually posted the solution to their idle problem.

It's doing the infamous idle hunt as the title said, I've been talking to yoshimitsuspeed about this but wanted to see if anyone else might have some insight as to the possible cause.

So I've got a 1974 celica with a jdm 4agze in it from an aw11 mr2 that I've converted to front engine rear wheel drive. All stock internals in the engine, I tore it down inspected and put back together with all new gaskets and factory torque specs. I've converted the stock aw11 intercooler to a front mount, ae86 headers, and the super charger from an AE101 with the smaller pulley. Single wire o2 sensor for the jdm aw11, a brand new denso one installed. Matching 1987 jdm aw11 ecu confirmed by part number 89661-17091.

Symptoms-
Starts up and idles fine in the cold start idle up cycle
Warms up and starts to idle down to 800-850rmp
Once it reaches operating temp it starts to hunt
Hunts for idle from 400-700rmp up to 1500-1700rpm
Eventually stalls itself out when it drops too low
You can stop it from hunting by gently caressing the revs down to idle around 900 or so
If you give it gas after stabilizing the idle it will either die when it tries returning to idle or ends up going into the hunt cycle again till it dies.
If you unplug the ISCV while it's running the idle shoots up to about 1250

What I've tried so far-
Engine is timed spot on
New o2 sensor, the first one was a brand new denso also but was pretty sooty from it running rich
New coolant temp sensor and throughly purged air from the cooling system
Reverse pressure testing the intake to fond vac leaks, found 5-6 small ones from my intercooler piping that i fixed
New throttle body, had a vac leak from the butterfly valve shaft so i replaced it with a unit w/o play
Calibrated TPS, all points within spec according to the BGB
Tired 2 different supercharger VSV's
Replaced ISCV with a used unit, both my original and the new ISCV measured 17.2 - 17.5 ohms when the BGB says it should be 16-17 ohms, could this be my issue?

All I can think of is the ISCV being garbage or more vac leaks that I can't find, anyone else have an ideas? I'd really appreciate any help, thanks everybody!

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Re: 4AGZE idle hunt problems

Postby jondee86 » Sat Feb 27, 2016 3:20 pm

Might be something useful in here...
http://www.mr2australia.com/mr2play/tm.aspx?m=103064

Symptoms sound exactly like a 4AGE (N/A) with a blocked waxstat, but I don't
know if those are used on the GZE.

Cheers... jondee86
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persists in trying to adapt the world to himself. Therefore, all progress
depends on the unreasonable man.

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Re: 4AGZE idle hunt problems

Postby GZE_RA21 » Sat Feb 27, 2016 8:45 pm

jondee86 wrote:Might be something useful in here...
http://www.mr2australia.com/mr2play/tm.aspx?m=103064

Symptoms sound exactly like a 4AGE (N/A) with a blocked waxstat, but I don't
know if those are used on the GZE.

Cheers... jondee86


Thanks for the input!

I did come across that in my searching, I used his technique of pressure testing the intake system to find vacuum leaks which worked very well, unfortunately I've fixed all but 2 extremely miniscule leaks, one from the new throttle body shaft and another from the replacement iscv that I highly doubt would cause such dramatic issues.

The GZE doesn't use the wax pellet IAC sensor like the 4AGE unfortunately, those IAC's may be expensive but they still exist. The GZE uses an Idle Speed Control Valve that has electronic input from the ecu to magnetically control an airflow passageway with a small valve between the the two ports on the sensor. They aren't interchangeable with any other vehicles and there don't seem to be any new ones, I even tried inquiring with Japanese parts distributors.

Really wishing I just got an N/A and threw a turbo on it about now..... :(

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Re: 4AGZE idle hunt problems

Postby jondee86 » Sat Feb 27, 2016 10:02 pm

The resiatance of the coils in the ISCV won't be that critical. One or two Ohms
over spec should not affect operation of the valve.

It's kind of interesting that you can stop the hunting by fiddling with the throttle.
This makes me think that the IDL switch in the TPS might be involved. Assuming
that the 4AGZE shares certain functions with the 4AGE, the IDL switch will be
letting the ECU know when the throttle is fully closed. The ECU will then change
from "engine driving" to "engine idling" fuel and ignition maps.

If the engine is trying to idle while on the "engine driving" map, it will most likely
become unstable. So although you said that you set the TPS to the book, did you
verify that the IDL switch output goes from continuity (closed throttle) to open
circuit when the throttle is opened slightly ? If it went from open circuit to continuity
that would mean you had crossed wires somewhere.

Of course if you are using an uncut factory wiring harness you should be OK, but
speaking from experience, it is quite easy to mess up when splicing TPS wires :oops:

Cheers... jondee86
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persists in trying to adapt the world to himself. Therefore, all progress
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Re: 4AGZE idle hunt problems

Postby GZE_RA21 » Sun Feb 28, 2016 10:55 am

Interesting, yes the tps differences between the GE and GZE are minimal. My harness has not been cut or tampered with regarding the tps, although I will investigate further to eliminate any possibility. I will continue checking the tps along with reading voltage inputs at the ecu and check for any inconsistencies with voltage specs.

This was copied directly from my BGB as to the specs the GZE tps is supposed to be tested at with feeler gauges between the throttle wheel and throttle set screw to check if it's within specifications, my tps was within these parameters when I tested it.

0 mm (0 in.) VTA - E2 0.2- 0.8 k - ohms
0.40 mm (0.0157 in.) IDL - E2 2.3 k - ohms or less
0.65 mm (0.0256 in.) IDL - E2 Infinity
Throttle valve fully opened position VTA - E2 3.3- 10 k ohms
Any position - Vcc - E2 - 3-7 k ohms

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Re: 4AGZE idle hunt problems

Postby jondee86 » Sun Feb 28, 2016 2:39 pm

OK... I'm only shooting in the dark, as if it was something easy to spot you
would have found it by now :) And it is only the logic of the IDL switch that
you could check if wires have been spliced. Test 0.40mm and 0.65mm values
at the ECU plug (plug out of ECU).

Other items that come to mind as possible causes are fuel pressure and
ignition timing. Again I assume that the GZE timing is set after shorting
a plug and putting the ECU into "diagnostic mode". Base timing set at
10deg BTDC then idling at 16-17deg BTDC warmed up and out of diagnostic
mode. Again, just double checking you on these points, as they are things
that get overlooked from time to time.

BTW... if you have driven the car on the road, how does the engine perform
apart from the stalling at idle thing ?

Cheers... jondee86
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persists in trying to adapt the world to himself. Therefore, all progress
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Re: 4AGZE idle hunt problems

Postby GZE_RA21 » Sun Feb 28, 2016 3:41 pm

First of I'd like to thank you for taking the time to help me out like this, i really appreciate the input and advise i feel like I'm slowly sifting through the problems one by one.

Checked resistance at the ecu terminals-
IDL-E2 had continuity when closed and deflected to infinity when opened
IDL-E2 @ 0.40mm measured 17.8 ohms
IDL-E2 @ 0.65mm measured infinity

So secondly, and I can't believe i forgot to mention this in the original post but fuel has been a concern of mine also as I had to convert the stock carbureted system to handle fuel injection.

What I started off with was replacing fuel lines with 5/16ths hard line from the pump to the engine bay, then a 1/4" to 5/16" reducer inline pre pump fuel filter to go between the pump and tank as the tank lines were only 1/4" for the carburetor 7psi stock mechanical fuel pump.
So I started with an inline electric fuel pump producing max 40psi, too weak because fuel pressure was dropping to 25psi under load.
Replaced with a max 90psi inline electric pump, worked but was straining to deliver fuel as there were bubbles being drawn into the inline pre filter.
Tried setting up a low psi electric priming pump to feed the main pump and prevent air from reaching the 90psi pump but with out any results, fuel pressure was still bouncing around from 35-42psi.
Tried a higher 125psi pump with out the priming pump but still got air in the filter, tried running the pump directly from a gas can with good results, had the tank modified to a 5/16" outlet to supply the correct diameter lines to the pump and it seemed to be working decent. With the new lines and outlet the pressure was still erratic and surging to 45 psi at idle, replaced the pressure regulator and now it reads consistently at the pressure gauge.
Now I'm wondering if there is too much fuel pressure from the 125psi pump perhaps? But the regulator is stepping it down to ~37-39 psi where it should be.
However a very strange thing is happening now, the idle increases if you shut the pump off while it's idling. (I have my fuel pump wired to a toggle switch for manual control) this idle increase when switching the pump off can be used to counteract the hunting idle when the revs drop too low and will actually stabilize the idle. I don't know what to make of this as it was just discovered last night.

Yes it's been timed correctly but I will re check that as well just to be sure.

I've driven the car all of once with the new engine, had to set the idle at about 1100-1200 to keep it from stalling mid-drive as the starter isn't controled by the key, still jumping pins to start it. It drove well, good power no hesitation, but when the throttle was released the revs wouldn't return to idle immediately, not sure if the supercharger was clutching on because i couldn't see my boost gauge (drove it at night) or hear it clutch on. I'm also unsure of my rpm as nothing but the engine harness is getting power, no lights, no instruments, etc.

Again, thanks for the help and ill check timing asap!

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Re: 4AGZE idle hunt problems

Postby jondee86 » Sun Feb 28, 2016 9:55 pm

Given the problems you had with getting the fuel supply to stabilize, it is quite
likely that you have a rich-lean hunt going on. I'm short on GZE reference material,
but I believe that the GZE has a standard Toyota 1:1 vacuum/pressure referenced
rising rate regulator. This means that if you have 37psi (engine OFF. pump ON),
you will have around 27-30psi at idle and around 45psi at 8psi of boost.

The manifold pressure reference (rubber hose) is designed to maintain a constant
pressure differential across the fuel injectors, so that the amount of fuel injected
per unit of time remains constant regardless of manifold pressure :geek:

There are other closed loop correction systems in action also... O2 sensor driven
mixture adjustment and the ECU controlled ISCV system. If the fuel pressure is too
high or unstable, it can screw with the operation of the closed loop systems. The
fuel mixture oscillates between lean and rich and the end result is hunting.

I'm gonna assume that your engine does not run for very long with the fuel pump OFF :)
But in the couple of seconds that it continues to run, the fuel pressure in the rail will
drop quickly, likely changing the mixture from rich to lean until all the fuel already
in the intake is consumed. This "could" account for the hunt stopping.

Cheers... jondee86
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persists in trying to adapt the world to himself. Therefore, all progress
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Re: 4AGZE idle hunt problems

Postby jondee86 » Mon Feb 29, 2016 1:01 am

Pumps are funny things... pressure alone is not usually a problem. After all, the
pressure in the line is governed by the resistance to flow, so the pump will not
deliver 90psi unless the line is almost closed off. Flow on the other hand, can be
a problem, if the amount of fluid trying to get thru a small pipe becomes excessive.

Resistance varies as the square of velocity. So a high-flowing pump (much larger
than required for actual engine fuel requirements) can create significant back
pressure in the return line. When this occurs the pressure differential across the
FPR is reduced, and the pump operating point will change. Basically the rail
pressure will rise until the FPR can flow the pump output (minus fuel consumed
by the engine). This is not a happy situation.

In your case I have no idea if this is actually happening. Watching the fuel pressure
gauge should provide sufficient information...
- Check the pressure pump ON, engine OFF.
- Start the engine and the pressure should drop when idling.
- Rev the engine quickly and the pressure should briefly rise.

The fuel pressure should respond quickly to changes in manifold pressure. If you
snap the throttle closed from say 3000rpm, the fuel pressure should immediately
drop to a value lower than idle pressure. If it does not, investigate why ??

Cheers... jondee86

PS: Again I have no special knowledge of how the GZE fuel system works. The above
comments are based how I would expect it to work if it is similar to the 4AGE system.
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Re: 4AGZE idle hunt problems

Postby GZE_RA21 » Tue Mar 01, 2016 1:46 pm

It's all starting to sound more likely to be a fuel issue than anything else. I tested ask the points at the ecu to measure the voltage received at the ecu connectors and everything was in spec with the excepting of one if the two iscv points -
with the ignition on and engine off spec is 9-14V
One wire measured 12.46v the other measured 0.77v, way off.

The other irregularity was the voltage measured from the tps with the throttle body at wide open throttle, spec is 4-5v and i measured 3.77v not off by much and i doubt it would have anything to do with the issues at idle.

I was testing these things while letting it warm up last night before going to re check the timing, with the pump on and engine off it was reading about 37psi, with the engine running it was about the same, 35-37 about. Once warmed up and dropping rpm from the cold start idle up it came down to 820rmp consistently at 35 psi. I couldn't believe it, it was running perfectly! After about a minute of disbelief it started missing then sputtered and died, it ran out of gas before i had a chance to mess with it anymore, but it did run great with less pressure. Could that mean my fuel pump is creating excessive pressure in the system?

I'm getting more gas after work to test some more.

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Re: 4AGZE idle hunt problems

Postby jondee86 » Tue Mar 01, 2016 6:19 pm

The best information I can find on the ISCV indicates that it is most likely a PWM
controlled 3-wire rotary solenoid valve, similar to the 20V ISCV. If this is correct,
then one coil pulls the valve open and the other coil pulls the valve closed. This
means that as the valve moves the voltage on one coil increases as the voltage
on the other decreases... kind of like a tug-o-war :)

When the engine powers up (key ON) it is likely that the ECU will command the
ISCV to drive to the wide open state in preparation for supplying extra air to
aid with engine starting. So you could expect to see around 12V on one coil and
next to nothing on the other.

For the time being I suggest you concentrate on sorting the fuel supply, as resolving
one issue at a time is the way to go. See what kind of pressure readings you get
with a couple of gallons of gas in the tank.

Cheers... jondee86
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Re: 4AGZE idle hunt problems

Postby GZE_RA21 » Tue Mar 01, 2016 8:16 pm

I was just going by the FSM that said both pins should be reading 9-14v but anyway, not trying to jump around just trying to eliminate anything easy to find.

So i got some gas and some pressure readings..
Readings are being taken from the rail with the pressure gauge connected to the cold start injector.
With the pump on and engine off its at 36-37 psi
At idle pressure is at 35-36 psi
Revving it to about 3000 then cutting throttle it dips down to about 31-32 psi.
Vacuum typically decreases when given gas, fuel pressure decreases when it's given gas.

It's still hunting and hard to get to idle but i checked the timing and it's at 10 BTDC in diagnostic mode, was being uncooperative after I took it out of diag, wouldn't idle at less than 1100. Checked the timing out of diag idling at about 1200, timing was about 20 BTDC.

Any ideas? Thanks in advance!

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Re: 4AGZE idle hunt problems

Postby jondee86 » Tue Mar 01, 2016 9:48 pm

Sure... not saying that there might not be some issue with the ISCV. I could be out
of court with my assumption of how it works. We can dig into that a bit more later.

The fact that your fuel pressure hardly drops at all when idling makes me think that
you will be running rich at idle. I recently had my car running extremely rich at idle,
it was as lumpy as hell... choking up and wanting to idle down and stall. Plugs were
covered in soot even though the car (N.A.) ran pretty good at high throttle openings
it was a real pig to drive around town.

The fuel pressure should increase when you open the throttle and lower the manifold
vacuum ( = increase the absolute pressure). Without being able to apply a sustained
load on the engine it may be difficult to discover if the drop in pressure is simply a
transient condition before rising, or something else. High engine speed in a stationary
vehicle requires only a little extra fuel above the fuel required at idle. And the manifold
vacuum will remain high due to the small throttle opening. So it could be that the small
increase in fuel required to hold a constant 3000rpm is just enough to allow the FPR
to gain a little bit of extra control authority.

That is (and here I am guessing), the FPR might be operating at the very edge of its
abilty to regulate the pressure... acting more like a fixed orifice where rail pressure
is set by the pump flow rate. The fact that the pressure does not drop as much as
expected when the engine is idling tends to bear this out. It would be interesting to
see what happens if you could cut the pump flow back by say 30%. If my theory is
correct, this should allow the regulator to regain control of the rail pressure, and
operate as expected.

Do you have any rubber hose in the fuel supply line that you could clamp down to
restrict the flow for a test ? For example, restricting the flow at idle should let the
pressure rail pressure drop and reduce the overfueling.

Cheers... jondee86

PS: Dang... I do like a good mystery :D
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Re: 4AGZE idle hunt problems

Postby GZE_RA21 » Tue Mar 01, 2016 10:05 pm

I will try pinching a rubber hose and record the pressure readings and look for any inconsistencies, I have a friend who works at an auto parts store who is going to do some digging around for a new fuel pump for me in the morning. My current pump is a 125 max psi and 38 gallon per hour pump, im looking at either trying out a 55 psi / 35 GPH or a 95 psi / 30 GPH pump as this is one of the last variables that hasn't been tested extensively. I'll take the readings with the current pump before i install a new one, thanks for the advise!

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Re: 4AGZE idle hunt problems

Postby jondee86 » Wed Mar 02, 2016 12:13 am

If your GZE was running WOT @ 100% duty cycle on the injectors and at full boost,
the engine would be requiring around 90 liters/hour (24 GPH) at around 45-50 psi.
In reality, the duty cycle should not exceed 85% on the factory ECU, so 20 GPH @
45-50 psi plus a bit of margin for wear and tear... say 35 GPH @ 55 psi ;)

A standard 4AGE in-tank pump is said to deliver around 85 liters/hour at 45 psi and
there are a lot of people who have run a 4AGZE swap on the stock 4AGE pump. The
stock 4AGE pump will will make about 75 psi when dead headed (no flow).

Cheers... jondee86
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Re: 4AGZE idle hunt problems

Postby GZE_RA21 » Sun Mar 06, 2016 11:17 am

Alright, so got the new pump and also a wide band o2 sensor to monitor AFR's to possibly find out if it's a lean condition idle hunt problem.

Unfortunately i didn't get a chance to take any readings while restricting the fuel flow by pinching a rubber hose with the old pump but this new pump seems to be working much better. No inconsistencies in the noise from the pump like there was on the old one.

However the pressure readings are showing similar results....
Engine off pump on fuel pressure is at 36psi
Engine idling pressure is right at 35psi
Quickly hitting the throttle when the revs drop low enough to stall the fuel pressure dips to about 27 psi then raises again to 35ish
If you rev the engine from idle pressure decreases to about 34 but stays in the 34-36 range while being revved
Its only if the revs drop too low to where it needs to be saved from stalling that fuel pressure drops a lot.
Pressure remains constant at 35 psi under any load with the vac line to the pressure regulator disconnected.

As for the AFRs i tried watching the display with the original denso o2 sensor feeding signal to the ECU then with the wide band supplying signal.
AFRs didn't vary much regardless of which o2 was supplying signal to the ECU. AFRs are consistent at 11 in open loop, once in closed loop the AFRs are right around 12.5, pretty rich for idle. Under load it goes to around 13 if you keep the revs around 2000rpm which doesn't seem off but with 12.5 at idle something isn't right.

Also got it to idle really well at around 850rpm for a bit and had the strangest thing happen a couple different times. It just died. No studdering no hesitation, almost like somebody just shut the car off. I've started looking into possible ignition faults.

Still hunting after receiving throttle input from a consistent idle, doesn't die but idles high ~1200rpm with the ISCV unplugged still.

Any ideas? Anything you'd suggest trying? I'm open to any and all suggestions. Thanks!

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Re: 4AGZE idle hunt problems

Postby s24a » Sun Mar 06, 2016 12:05 pm

Can you state again what the diameters (and lengths) of the fuel line TO the engine and the return line FROM the pressure regulator are?
Also, do they vary in diameters along the runs?

Reason is that the fuel pressure should go UP when intake vacuum goes towards atmospheric or above (with hose on vacuum port of the regulator). In your case it is dropping which is not a correct condition. The O2 sensor may also not be getting good ground as you are indicating richer than stoichiometric, which leads me to believe that the voltage is offset to the low (rich) side. It should at idle switch rich/lean/rich at around 7-12Hz as a low frequency to as fast as 16-20Hz if the sensor is fresh and engine is hot.
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Re: 4AGZE idle hunt problems

Postby GZE_RA21 » Sun Mar 06, 2016 1:12 pm

5/16" lines from the tank to the rail, 1/4" return lines from the regulator to the tank, they do not vary in diameter, ask 5/16 from tank to rail and all 1/4" on the return. Not sure as to the exact lengths of the lines but it's all hard line with short lengths of fuel injection rated hose connecting everything. I can get lengths later today and post them here if you'd like.

Could some sort of vacuum leak be causing the regulator to drop instead of increase fuel pressure while revving it? The FPR is brand new also, although it was for an AE86 not the S/C AW11 as the FPRs for the 4AGZE have been discontinued, the difference in allowed fuel pressure was only 1psi (39 instead of 38psi) could this be any sort of an issue?

The original denso o2 sensor is a single wire o2 that i believe grounds out to the manifold it's bolted to, it's a single wire o2 sensor because the engine is an 87 4agze Japan import with a matching ecu confirmed by part number and compete lack of any egr anything on the engine.

As for the wide band, I have it on its own circuit running directly to the battery with an inline fuse and toggle switch and it's grounded directly to the battery to chassis grounding point so I know that's grounded properly.

Both sensors are brand new and those readings taken were with the engine hot.

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Re: 4AGZE idle hunt problems

Postby jondee86 » Sun Mar 06, 2016 4:15 pm

GZE_RA21 wrote:Alright, so got the new pump and also a wide band o2 sensor to monitor AFR's
to possibly find out if it's a lean condition idle hunt problem.

From what you have observed, your FPR appears to be functioning, only acting
opposite to what might be expected. When you whack the throttle open, the
fuel preesure goes down instead of up ?? And at idle. the pressure does not drop
at all... rather unusual :?

However, if the fuel pressure is higher than it should be at idle, then your AFR
will be richer than it should be... no mystery there. So now to address the question
of WHY the pressure does not drop.

Easiest test is to take the engine to a higher rpm (say 3000) hold steady and then
allow the throttle to snap shut. This will create high manifold vacuum, and the the
fuel pressure should momentarily drop 8 or 10psi below idle pressure. A more
technically correct test would be to get a Mityvac and connect it to the FPR vacuum
hose. Slowly pull a vacuum and observe both the fuel pressure and AFR.

Note, I have not been able to find any credible reference that shows me exactly
where on the 4AGZE intake the FPR vacuum hose is connected. Because of the
proliferation of small hoses, and the fact that this is a supercharged engine, it
may be possible to connect the FPR vacuum hose to the wrong part of the manifold.
Or there may be some ECU controlled VSV, bypass valve or other trickery that makes
changes to the intake system when the throttle is snapped open.

Cheers... jondee86
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persists in trying to adapt the world to himself. Therefore, all progress
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Re: 4AGZE idle hunt problems

Postby GZE_RA21 » Sun Mar 06, 2016 4:25 pm

Slight update, upon further inspection the vacuum hose going to the vsv that should increase fuel pressure from the regulator was connected to a vacuum port on the intake that may have been partially blocked when we flipped the intake elbow on top of the throttle body 180° to face the front of the car. This line wasn't getting much vacuum and wasn't allowing the vsv to control the FPR, after switching the vsv hose to another vacuum port the fuel pressure at idle sits around ~26-27 psi and increases past 30 psi when throttle is applied and vacuum gets closer to atmospheric.

When idling consistently, if it's given throttle input it will still try to stall out when the revs drop back down, but it doesn't surge up so much really, more just stalls out on its way back down to trying to idle, maybe the ISVC is just part of the problem now?

AFRs are better now at about 13-13.5 so closer to stoichiometric but still rich, maybe the AFM could be out of adjustment? I noticed the grommet that covers the adjustment screw is missing and there appears to be marks from a screwdriver inside the bore that screw is in. I've tested the voltage output from the AFM to the ECU and everything is within spec, but could that adjustment screw being tampered with have something to do with the rich condition?

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jondee86
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Location: Wellington, New Zealand

Re: 4AGZE idle hunt problems

Postby jondee86 » Sun Mar 06, 2016 7:33 pm

Progress :D Now you have the fuel pump and FPR sorted.

AFAIK there are two ways to mess with the AFM. There is the idle air bypass screw
which sets the idling position for the flap inside the AFM. Then there is fiddling with
the clockspring inside the (should be sealed) AFM cover. This adjustment fools
the ECU into thinking that the flap is open further than it actually is, and so the
ECU adds extra fuel making the mixture richer across the board.

If the ISCV is similar to the 20V 4AGE, then it is factory set and sealed... not user
adjustable. However, there is a misconception that bad idle can be miraculously
cured by randomly messing with factory set components. In this case it is possible
that someone opened the base of the valve and tightened or loosened the bi-metallic
spring. It may be possible to test the valve by applying 12V first to one coil and then
to the other while blowing thru the valve.

A clean valve should go to the end of its travel and audibly "click" as it hits the end
stop. When the valve is wide open, there should be no restance to airflow. When it
is fully closed there should be no airflow. Never having seen a GZE valve. I don't know
how easy it will be to do the "blow thru" test. And cleaning the valve is always a good
idea, as they can get clogged with crud if breathing crankcase fumes.

Cheers... jondee86
The reasonable man adapts himself to the world; the unreasonable one
persists in trying to adapt the world to himself. Therefore, all progress
depends on the unreasonable man.

GZE_RA21
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Location: San Clemente, California
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Re: 4AGZE idle hunt problems

Postby GZE_RA21 » Sun Mar 06, 2016 10:58 pm

After adjusting the AFM air by pass screw located on the body of the AFM while the engine idled I managed to get the air fuel ratio to hold steady at stoichiometric, or at least varying between 14.5 to 15. With the AFRs at s much better level and idle adjusted to about 900rpm it was running extremely well. When the engine received throttle input it would catch itself before stalling and return to idle at 900. This happened consistently, if it idles less than 900 it would be very close to stalling after throttle input but would still save itself. I'm thinking the ISC is operating just not at its proper levels, but it's running very well now.

Image

This is the 4AGZE ISC from the FSM, im not sure how different the ISC on the 20v is but i bought a used ISC to see if it would be within spec compared to mine but it was not. I used the closer to spec ISC, cleaned it out very well with intake parts cleaner, tested it with supplying 12v to both pins on the valve itself to confirm operation which it was, with an audible metallic click in both directions. The valve still gave out of spec voltage readings when measured at the ecu.

Thank you for helping me out and all the advice you've given its been a huge help!

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jondee86
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Posts: 2910
Joined: Fri Jan 11, 2013 10:21 pm
Location: Wellington, New Zealand

Re: 4AGZE idle hunt problems

Postby jondee86 » Mon Mar 07, 2016 1:20 am

Congratulations !!! No more hunting at idle :)

The configuration of the 20V ISCV is quite different, but the operating principle
is the same. If the resistance of the two coils is the same, then they should respond
in a similar manner when the ECU applies power. I don't know how the voltage varies
with the valve position, but I would expect that the only time the voltage on the two
coils would be the same is when the valve is at its travel midpoint (rest position).

Many engines (including the 4AGE) like to idle a bit richer than stoich. You can try
a few different settings and see what works best for the GZE.

Cheers... jondee86
The reasonable man adapts himself to the world; the unreasonable one
persists in trying to adapt the world to himself. Therefore, all progress
depends on the unreasonable man.