GUIDE: ISCV Wiring / M-REL Wiring

[wilbo666]

It seems that one of the hardest things for people to get right when doing an engine conversion into an older car is the ISCV wiring.
As a result I've decided to put together this little guide in the hope that it can help others with their ISCV wiring.

This guide is going to focus on the "6 wire" ISCVs as found on 7M, 1JZ, 2JZ and other engines, however it will apply in some extent to all ISCVs.


ISCV Function:
The function of the ISCV (Idle Speed Control Valve) is to allow the engine to maintain the correct idle speed as determined by the engine ECU, regardless of engine temperature, AC On/Off, electrical loads, etc.

The ISCV achieves idle control by providing a path for intake air around the throttle, this effectively acts to open the throttle and allow more air in leading to raised idle.

On turbo applications a one way valve is installed so that boost pressure cannot exit the plenum / after the throttle body. The one way valve is ussually a little disk with a rubber flap.


ISCV Operation:
The 6 wire ISCVs use a stepper motor to control a plunger that determines how "open" or "closed" the ISCV is.

How much air bypasses the throttle determines how much the idle is raised by. (More open = higher idle).


ISCV Wiring:
Power is supplied to the two center pins (pin 2 and 5) of the ISCV and the engine ECU grounds the stepper motor coils (connects them to ground) in the correct order to open or close the ISCV as required to raise or lower the engines idle.

The power that is connected to the ISCV is via the main EFI relay which is controlled by the ECU M-REL pin to stay powered up for a few seconds after the engine is switched off, keeping the ISCV powered after the engine has been switched off. The ISCV is NOT powered by a switched ignition source or relay and doing this will result in incorrect ISCV operation / idle issues.

Upon turning the engine off, the engine ECU and the ISCV (among other items) remain powered for a few seconds to allow the ISCV to be fully opened. This is done for at least two reasons which are listed below.

1. To 'reset' the ISCV - The engine ECU needs to know what position the ISCV is in to be able to control it correctly.
2. To enable the engine to start easier - ISCV fully open = highest idle upon start up.

The way in which the engine ECU remains powered after turning the engine off is via the M-REL output pin on the engine ECU. The below diagram shows how the system is wired.

In short:

• The engine ECU knows when the ignition is on via the IGN pin on the ECU (Receives +12V when ignition/crank is on)
• The engine ECU turns the main EFI relay on via the M-REL pin on the ECU when the ignition is on
• The M-REL output supplies +12V to the main EFI relay to turn the main EFI relay on
• When the main EFI relay is on +12V is connected to the engine ECU, ISCV, etc to power them
  
• When the engine is started the engine ECU knows the ISCV is fully open and closes it as required after engine start up to achieve the desired idle
• During normal operation the engine ECU continues to open and close the ISCV small amounts to maintain the desired idle
  
• When the ignition / engine is switched off the engine ECU continues to power the main EFI relay via the M-REL engine ECU output, this allows the engine ECU time to fully open the ISCV (reset it), allowing it to function correctly.
• After the ISCV has been fully opened the engine ECU turns the main EFI relay off to disconnect power from the engine ECU, ISCV, etc

References:






http://www.cygnusx1.net/Supra/Librar...spx?S=FI&P=106
http://www.cygnusx1.net/Supra/Librar...spx?S=FI&P=107

Autoshop101 Reference: 25 Engine Controls #2 - ECU/Outputs.pdf file size 495KB

Cheers
Wilbo

[Gavatron]

Nice guide Wilbo. Can't rep you again. It's simple enough, but it seems to screw a lot of people around.

[jameschia2722]

Hi Wilbo,

may i know if my iscv from 1jz vvti with the reading resistance: b1 - s1 or s3 47ohm
b2 - s2 or s4 46.7ohm

base on your guideline, it suppose to read between 0-30ohm.
is it a faulty iscv? i have tested another used iscv as well and the reading also same 46.8ohm -47ohm

i cant get my car coldstart every morning, it suffer me almost a year... sad.

[td42gq]

Nice guide Wilbo, top effort.

Might be worth a mention that if your wanting to use a 6 wire iscv (like on the 1jz) with a haltech or some of the other aftermarket ECU's the 2 middle pins B1 & B2 and not required to be used and therefore the power relay is not required. The haltech does all the work for you.

[td42gq]

In repsonse to your question jameschia2722 i would think that your iscv internal coils are ok. It is more important that they are all around the same than wether or not they are within the 10 - 30 ohm. In my experience the ones that don't work will either be open circuit or the plunger will be seized, the internal coils will sometimes meaure slightly out of range but are generally still in good working condition.
I hope that helps
Aaron

[wilbo666]

Hi Wilbo,

may i know if my iscv from 1jz vvti with the reading resistance: b1 - s1 or s3 47ohm
b2 - s2 or s4 46.7ohm

base on your guideline, it suppose to read between 0-30ohm.
is it a faulty iscv? i have tested another used iscv as well and the reading also same 46.8ohm -47ohm

i cant get my car coldstart every morning, it suffer me almost a year... sad.

As td42gq says, I wouldn't be concerned about the resistance being different from what I posted. The 10-30Ω value listed is for MA70 and it is quite possible that vvti 1jz is slightly different, the fact that you have measured two different ISCVs and had the same result would support this

Have you checked to see that the ISCV B1 and B2 pins are powered? And that the B1 and B2 pins stay powered for a short amount of time after the engine has been switched off? I.e. you have wired M-REL correctly

Secondly have you tried following the steps listed in the service manual to 'manually' step open / close the ISCV?

Might be worth a mention that if your wanting to use a 6 wire iscv (like on the 1jz) with a haltech or some of the other aftermarket ECU's the 2 middle pins B1 & B2 and not required to be used and therefore the power relay is not required. The haltech does all the work for you.

Personally I think that would just add to the confusion for some people!

Cheers
Wilbo

[jameschia2722]

As td42gq says, I wouldn't be concerned about the resistance being different from what I posted. The 10-30Ω value listed is for MA70 and it is quite possible that vvti 1jz is slightly different, the fact that you have measured two different ISCVs and had the same result would support this

Have you checked to see that the ISCV B1 and B2 pins are powered? And that the B1 and B2 pins stay powered for a short amount of time after the engine has been switched off? I.e. you have wired M-REL correctly

Secondly have you tried following the steps listed in the service manual to 'manually' step open / close the ISCV?





Personally I think that would just add to the confusion for some people!

Cheers
Wilbo

Wilbo,

Yea, i have tested the iscv with the steps u post, and its work fine.
And i have wired M-REL as what you posted with a relay to current in main EFI.
The B1 and B2 dint stay on for 1 or 2 second while turning off iginition. signh..
Any idea troubleshoot?

[wilbo666]

Wilbo,

Yea, i have tested the iscv with the steps u post, and its work fine.
And i have wired M-REL as what you posted with a relay to current in main EFI.
The B1 and B2 dint stay on for 1 or 2 second while turning off iginition. signh..
Any idea troubleshoot?

Have you double checked that the ISCV pins B1 and B2 are actually connected to the power that is switched by the M-REL switched relay?! Maybe you're powering the ISCV off the wrong switched power source?

Have you also checked to make sure that the main EFI relay that is switched on and off by the engine ECU M-REL pin is staying on for a few seconds after the ignition switch has been turned off? If it isn't perhaps something else isn't wired to the engine ECU correctly? (Maybe BATT or IGSW...)

Cheers
Wilbo

[jameschia2722]

wilbo,

thanks boss, i will check up the wire again... hope i get the right sign from m-rel signal..

[50RTD]

Great write up Wilbo, thank you!

I would be very interested in how one would go about wiring an ISCV in a basic aftermarket computer, such as a Microtech or EMS Stinger for example?

I've also read about crudely wiring an ISCV to a manual switch, that would be switched on during cold starts etc... is this possible with a Toyota ISCV? Although crude, it must be better than deleting the ISCV as many people do?

Cheers!!

-Dan

[wilbo666]

I would be very interested in how one would go about wiring an ISCV in a basic aftermarket computer, such as a Microtech or EMS Stinger for example?

I don't have any first hand experience with either of those, but at a quick glance they don't look to cater for 6 wire ISCVs

I've also read about crudely wiring an ISCV to a manual switch, that would be switched on during cold starts etc... is this possible with a Toyota ISCV? Although crude, it must be better than deleting the ISCV as many people do?

Cheers!!

-Dan

Not possible with the 6 wire Toyota ISCVs, at least not without somewhat complex external hardware to control the 6 wire ISCV I'm afraid.

Cheers
Wilbo

[jameschia2722]

Have you double checked that the ISCV pins B1 and B2 are actually connected to the power that is switched by the M-REL switched relay?! Maybe you're powering the ISCV off the wrong switched power source?

Have you also checked to make sure that the main EFI relay that is switched on and off by the engine ECU M-REL pin is staying on for a few seconds after the ignition switch has been turned off? If it isn't perhaps something else isn't wired to the engine ECU correctly? (Maybe BATT or IGSW...)

Cheers
Wilbo

Yo boss,

Thank you, and i have found out my B1 n B2 connected with all others injector + signal with IGSW control. And i hav reconnect all with M-REL signal relay and the ISCV work great, but then i need to seperate out the injectors signal due to engine stay starting 1-2 second to shut down when turning off engine.

Beside, while checking my engine looms, i think i have misconnect a wire which gived signal to combination meter wher check engine light, oil pressure light n oil level light appear before start up the engine. May i know how i gonna truoble shoot it? (im so headace to open out all over again.)

[bk_]

And for future reference for those with aftermarket ECUs (eg: HKS F-CON V PRO) with a non-piggyback harness:

ISCV:
* connect ISC1 to +A (HKS pin 37)
* connect ISC2 to -B (HKS pin 30)
* connect ISC3 to -A (HKS pin 29)
* connect ISC4 to +B (HKS pin 28)

M-REL
* connect IGSW input to M-REL output on harness end. And connect switched powered to M-REL. (sounds like a hack,but is there a better way?)

note: unfortunately on the (v3.2+) HKS, you can either control S/M ISCV or have M-REL output, not both. there is no M-REL option on v3.1 or lower.