1JZ Idle issues - weird ISCV behaviour.

[Aether]

Hi guys,

Have an idle issue which has been present since I rebuilt the motor and put everything back in...
I have read through numerous threads from many forums about testing the ISCV valve and what the problem could be, but still the problem persists.

I have confirmed ISCV valve operation in the sense that when the ignition is switched on, 12 volts appear at B+ & B1+ terminals of the ISCV valve, also once the ignition is turned off, M-REL maintains power to B+ & B1 for a few seconds and you can hear the ISCV clicking as it resets.

Have taken the ISCV valve off, connected the plug, started the car and switched it off and you can see the valve inside the ISCV move forward and back as it is meant to be, so I am gathering that the wiring and the ECU is working fine from that perspective.

Now this is where it gets weird, with the ISCV in place but with the connector unplugged (car is cold), I start the car and it revs up to 1800-2000rpm, but idle hunts...whilst the car is running I connect the ISCV connector, idle no longer hunts and stays high at 1800-2000rpm, and as the car begins to warm up the idle drops as it is meant to, and it seems to work perfectly. Next morning I go outside with the connector to the ISCV connected form the night before, start the car and the car idles only at 900rpm, no cold start! Do the same thing as mentioned above and it works until the next morning again???

The car is running an EMU piggy back and I have the water temp sensor going through the EMU before it reconnects to the plug and play loom...could that be causing any issues...?

I believe the ISCV is controlled/adjusted by a number of external sensors, could anyone shed some light if this is true or not and if they could be affecting the cold start idle?

Any help would be appreciated as I have been trying to put this issue to rest for the past year.

** I have also tried another ISCV valve and also replaced the ECU with another known working one...process of elimination...but the problem behaves exactly the same way.

Cheers,

[Daddio]

ECU takes a signal from the ECU temp sender (not the gauge temp sender) then adjusts IACV to compensate for cold idle. Running the ECU temp signal through the EMU could be affecting the reading given to the ECU from the temp sender (ie the additional resistance could be enough for the ECU to not 'see' a cold engine) Perhaps try a quick bypass of the EMU and see if that fixes the cold idle issue?

[dumbass]

is it in a factory setup or in a conversion
most issues with idle motors is they are either stuck or seized
or the ecu is not wired properly and it doesn't reset the idle motor when the engine is turned off for the next start the next morning
also do what daddo says and bypass water temp
those emange ecus cause all sorts of headaches

[Aether]

Thanks guys, it is in a factory setup so wiring should all be good apart from piggyback EMU...will set it up so the water temp bypasses the EMU, and goes directly to the factory ECU. Will post back results soon, hopefully will be able to do later on today. Thanks.

[Daddio]

For info, idle is adjusted by three signals that I know of: 1. ECU temp sender (for engine temp), 2. Battery voltage (high electrical load drops voltage and the ECU increases idle, eg when headlights are on), 3. A/C idle up takes a signal from the a/c compressor clutch (idle up for obvious reasons!) None of these will work correctly if the TPS is not set correctly and working properly. TPS seems to be the most common issue (apart from intake air leaks and dodgy AFM's) with getting a solid idle. Given you hear/see the IACV open fully at shut off, this suggests the TPS is working and adjusted correctly

[bk_]

As far as I know, IACV steps is not determined by battery voltage.

There's usually two main tables, regardless of ECU (OEM or aftermarket):
* ECT vs steps
* ECT vs target RPM, which is used to learn another table, ECT vs delta steps. If OEM ECU is reset, then this is all zeroes.

Offset of steps (and different target RPM for the first two) is determined by:
* A/C switch
* neutral switch (which also works with "dashpot trim" control)
* start compensation which is the initial IACV steps to open before start, relative to ECT vs steps table. This is only used prior to start.

TPS idle switch also determines whether to use idle ignition table, or main ignition table.

You shouldn't be intercepting the ECT sensor signal. From my experience with piggyback ECUs, the signal is only spliced (and read by ADC). OEM ECUs use a voltage divider (Toyota OEM use ~2680 ohms for +5V-INPUT, and the sensor itself provides the other resistor as part of the voltage divider)

Hope that helps.

[Aether]

Thanks guys, only reason I was intercepting the water and air temp signals was becuase of the T13 piggyback harness (plug and play)...I will disconnect the EMU from intercepting those two signals and run them directly to the ECU.

Now you mention the TPS as well, I had the TPS removed awhile back whilst detailing the throttle body (probably a big mistake), and even thou I had it replaced and tried to calibrate it as per the process in the manual...I am wondering if that may be the problem in that it is still not calibrated right?

The car tends to have a ghost rpm limit or breaks up between 6000-6500 rpm, like it hesitates and then wants to go...and supposedly I read last night that this can be a sign of an uncalibrated TPS?

I have tried everything from another ISCV, ECU, New water and air temp sensors etc...only thing I haven't tried is another untouched throttle body/TPS sensor...so I guess that is next on th elsit...is the TPS really that sensitive to calibrate/adjust?

[bk_]

Back when I had OEM ECU, I know the rotation of the TPS was really sensitive to when TPS idle switch would trigger / not trigger. But that's only because I usually drive around at 1500-1700 RPM.

But any higher RPM than that, is not going to be a TPS issue.

[Aether]

Hmmm, thanks for the replies...will change the throttle body and TPS with an untouched factory one and see what the results are...just find it weird that when I disconnect the ISCV connector and reconnect it at cold start-up that the cold start operation works, and then if I leave it for the night and try to start it in the morning...no cold start...

[bk_]

Since no ECT signal goes to OEM ECU (it was re-wired(??) to be direct to emanage, instead of spliced/tapped to emanage), OEM ECU thinks it's 80C (failsafe condition).

You can confirm this by checking OEM ECU error codes for ECT sensor failure.

There are only two scenarios of how to connect ECT in piggyback:
1) spliced/tapped to aftermarket ECU, with pullup resistor DISABLED.
2) secondary ECT sensor (either toyota OEM or generic), connected directly to aftermarket ECU, with pullup ENABLED.

Either of the above will need the correct voltage vs ECT table set.

I haven't heard of a scenario where ECT output signal is to OEM ECU.

Output signal of AFM (voltage or frequency based) or MAP or speed sensor to OEM ECU, yes, but not ECT/IAT.

[Aether]

bk_, what are you referring to with ECT? I understand that ECT is (Electronic Controlled Transmission) would I be right? If so the Auto is connected exactly the same way it always has been from factory...and am not intercepting any signal from that...if ECT you are mentioning is in reference to something else can you please explain a little further?

Everything on the car is in a factory setup, except the after market ECU being the E-manage Ultimate piggy backing to the Factory ECU via a T13 plug and play harness...and as mentioned above water and air temp sensors are now going direct to the factory ECU and is not intercepted via the EMU.

I got a replacement throttle body with TPS set from factory, and the same problem is occurring...car will not raise idle at cold start...poor and rough idle...so I don't think it is TPS related.

I did notice something new thou, start the car and it idles low and poorly, turn the car off and restart, same thing...but if I disconnect the ISCV connector whilst the car is running, and then take the ISCV off and look at the valve inside the ISCV, it is 100% closed. For some reason the ECU is not telling the ISCV valve to open at startup, thus why such a poor and rough idle.

I checked the ISCV whilst not connected to the throttle body and the ISCV valve is closed whilst the ignition is on and the car is running (cold start), when I turn the ignition off the valve inside the ISCV opens fully, start the car and the valve shuts completely??? So the ISCV valve is working fine and is not stuck, also it must be receiving the correct voltages at B+ & B1 and the S1-S4 pins, cause it opens and closes.

Appreciate your help...

EDIT: If I am not mistaken B+ & B1 receive 12V from M-REL, and then the ECU grounds pins ISC1-ISC4 to open or close the stepper motor in the ISCV, so it must be something else informing the ECU to shut the ISCV upon starting.

[Daddio]

He is referring ECT as Engie Coolant Temperature I think....
In simple terms: The IACV opens fully at shut down (for next start) after recieving a TPS closed signal. On start the ISCV is fully open, and is modulated towards closed by the ECU (provided the TPS sends a closed signal) The ECU reads engine temp (ECT) and RPM and adjusts accordingly. If ECT or RPM is missing (or TPS does not send closed signal) the ECU wont do anything.
Only way I can think the ECU will close the ISCV too far (ie closed) is if the RPM signal is corrupt or possibly absent? This is speculative as I am unsure.

[bk_]

ECT I mean Engine Coolant Temperature. I'm so used to calling it ECT rather than CTS (coolant temperature sensor)

[Aether]

Thanks Daddio, some good feedback in regards to the RPM signal, as I did some looking around and found the below in which a member advises the same thing, no RPM signal within 1 sec of starting seems to cause issues with the ISCV valve. I know for sure that the RPM signal and the TPS signal are also being intercepted by the EMU before going to the ECU...as the mapping in the EMU is based of them.

http://www.supraforums.com/forum/sho...-cold-start-up

Will do some playing around on the weekend and see what the go is...best option I think is to splice and tap as per bk_...but why release a T13 plug and play harness which intercepts the signals if it causes so many damn problems...grrr

Thanks,

[bk_]

TPS should be tapped/spliced.

Not sure why RPM would be intercepted - it's an OUTPUT signal to the tacho, nothing else.