ISCV Cleaning (*May* solve poor/erratic idle)

[The Witzl]

here's where it is on a silvertop 20v

[The Last Streetfighter]

Karl, what's wrong with your Pic?

[The Witzl]

that server is temporarily being ghey.

[brum]

Is there any pro/cons by not running the iscv? what happens if u disconnect it and manually adjust idle?

[old_mr2]

This is a great thread. Thanks Lambolica. This is my first job when my AW11 gets out of impound. Only 85 more days to wait!

[Grant]

Sometimes the problem is actually inside the stepper motor though. I pulled mine apart and found the worm thread tacky. Cleaned it with WD40 and a rag, applied a very light coating machine oil, gave it a quick spray of WD again and it worked fine.

[The Witzl]

I much prefer Inox over WD40 though, i've found it cleans up the gunk much better than WD40 and is just as good as machine oil.

But i just love Inox.

[Toyo Truck]

Lambolica,
top work on the write-up mate...+rep for you buddy!

I recently cleaned the ISC valve, but not the housing it goes into (off plenum)
It fixed most of the problem, but occaisionally it idles a bit rough.
I reckon you can tell when you need to clean the ISCV by switching on and off the A/C at idle. As soon as you turn the switch off/on, you can feel it in the motor, it drops to like 300-500rpm then goes back up (somethimes) to 1000rpm odd. I have 2 of these
valves at home, a dirty one and a fully cleaned one, I have tested them both in my car without actually cleaning out the housing they bolt into and this is what I have found.

One thing I can't work out, is when the car starts to idle badly, when I accellerate, I can
feel the motor sort of spluttering just a little as it goes from like 2000-3000 RPM?
do you think this is related somehow to the ISCV or is it probably something else like a
dud injector or something. I just suspect the ISCV as this problem only happens when the
idle goes bad.

brum,
I tried doing this dude, and it will run, but not really well hey.
I disconnected the ISCV while leaving it connected to the plenum...
The car starts idle at about 1500rpm then climbs slowly upto like 2300rpm then
it suddenly drops to 1000rpm and then climbs slowly back up to 2300rpm then drops again. My mate says this is the ECU running on "limp" mode or something?
As we had to do the same thing on his 1JZ-GTE cressida.
You can drive it like this, but it'll be noisey though!

Cheers,
Bart

[andy]

i removed the what was pictured above as the iscv to clean it and what not.
is this it? (dont forget its a silver 20v)

[Mos]

brum,
I tried doing this dude, and it will run, but not really well hey.
I disconnected the ISCV while leaving it connected to the plenum...
The car starts idle at about 1500rpm then climbs slowly upto like 2300rpm then
it suddenly drops to 1000rpm and then climbs slowly back up to 2300rpm then drops again. My mate says this is the ECU running on "limp" mode or something?

Hi Bart,

What you're experiencing is most likely idle rev limit or idle rev cut, whichever way you wish to look at it.

My understanding is as follows: with the IDL switch in the TPS closed (with a closed throttle body) the ECU allows a certain range of idle speed. If the rpm rises above this range the ECU fuel cuts until the rpm comes back down into allowable range. Hence the 1000-2500rpm "bouncing".

If you disconnect your stepper motor based ISCV (black thing with 6 pins in Simon's photos) on a non-running engine, the valve is fully open (read on for reasoning) allowing a large amount of air past the throttle, causing a unusually high idle rpm that is outside the ECU's permissible limits.

Never having tried it I'd hazard a guess that if you disconnected the ISCV cable while the engine is running it will not experience this bouncing, but the engine is likely to be harder to start.

This type of idle speed control is also used as an initial idle up on engine starting. If you study the wiring diagrams of an engine equipped with a stepper motor idle speed control valve you will notice that the ignition switch "switches on" the ECU, which in turn "switches on" the EFI relay powering the rest of the circuitry, including the main power to the ECU.

This way, once switched on, the ECU can determine when it will turn itself off. When you turn the ignition switch to off, the engine will shut down but the ECU will remain switched on through the EFI relay and will open up the idle speed control valve to its open position before shutting itself down. This can be verified by listening to the ISCV following a shutdown, as well as measuring the +B voltage on the diagnostic connector (output of EFI relay) - it will remain on for a few seconds after ignition switch shut down.

The purpose of this is to open the ISCV to facilitate starting of the engine.

Mos.

[Mos]

i removed the what was pictured above as the iscv to clean it and what not.
is this it? (dont forget its a silver 20v)

Andy,
What you have removed is just the solenoid itself - it causes the small metal drum to rotate (through an angle much less than 360). The rest of the valve is on the other end of the shaft the drum is on, inside the alloy assembly.
HTH.
Mos.

[andy]

Andy,
What you have removed is just the solenoid itself - it causes the small metal drum to rotate (through an angle much less than 360). The rest of the valve is on the other end of the shaft the drum is on, inside the alloy assembly.
HTH.
Mos.

thanks MOS, is it inside the block? sorry for the dumb questions but i cant get my heard through to see whats there.

[Mos]

thanks MOS, is it inside the block? sorry for the dumb questions but i cant get my heard through to see whats there.

It's inside the aluminium block that the solenoid bolts to. The drum that you can see is on an axle that extends maybe a inch into the block and has another small drum on the other end with a sort of wing that can block or open up an air passage. The theory of operation is the same as a 4A-GZE and 3S-GTE but I have no idea how to remove it off the 20V - you could try undoing that bolt (looks like 12mm?) visible in the photo and any other required to remove that block and have a look inside.

Mos.

[The Last Streetfighter]

Andy: Did you finally get this done?
Anyone else had any luck with doing their 20V one?

[andy]

nahh, i turned out my problem was dirty throttle bodies. its a pita to clean then, as the plenum needs to come out and apart. and then unless u take them totally off you cant get them totally clean.

now 6 months down the track it needs a clean again.