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With this guide, you'll have your silvertop's ISCV out in under 15 minutes, and you don't even need to remove your throttle bodies or plenum!But first, some theory......
The silvertop ISCV motor, like many Toyota ISCV's, is a twin-coil, rotary solenoid system. The ECU provides varying signals to the two coils that makes the valve open and close. By providing a stronger signal (faster pulses) to one coil, the valve will open, provide a stronger signal to the other coil and it will close. By varying the pulses to each coil, the ECU can position the valve wherever it likes.
So what does that mean for us?
Well, if the ISCV becomes choked up with junk, the valve wont open or close properly, and can even become jammed in one position. This happens more regularly that we would like on the silvertop, necessitating regular removal and cleaning.
Also, what I have found with this ISCV, is the spring inside seems to become annealed by the heat cycling of normal engine use. What this means is, when you take a piece of hardened or spring steel, and heat it up then let it cool over and over, it looses it's hardness or springyness.
How does that affect us? Well, the spring in the ISCV is used to adjust the minimum amount the ISCV can close. When the spring looses it's springyness, it allows the valve to close too far, the engine can't get enough air, and your car drops idle speed or even stalls.
From Shano2:
Quote
Typically the problem with the 20V's idle (at least here in Australia) is that as a result salt residue / corrosion from the shipment of front cuts from Japan they tend to seize up pretty easily (seen at least 6 seized). Most people don't know this is a problem so they hook the engine up and drive it without any preventative maintenance beforehand.
The valve is operated by a simple electro-magnetic coil which is controlled by the ECU amplifying the signal to either side of the coil to either increase or decrease the idle as required. When the valve is siezed the ECU keeps amplifying the signal more and more to change the idle but as long as it's working against a siezed or stiff valve it will eventually burn out the amplifier / transistor which controls the idle. This is, more often than not, the cause of 20V low idle problems.
The valve is operated by a simple electro-magnetic coil which is controlled by the ECU amplifying the signal to either side of the coil to either increase or decrease the idle as required. When the valve is siezed the ECU keeps amplifying the signal more and more to change the idle but as long as it's working against a siezed or stiff valve it will eventually burn out the amplifier / transistor which controls the idle. This is, more often than not, the cause of 20V low idle problems.
So how do we fix all this? (I'll add the transistor info once I've done some further information)
Read on.
First Step:
Remove your intake pipe and airbox etc up to the plenum chamber. This will expose the plate holding a heap of vac lines that the engine hook is also fitted to.
Disconnect all the vac lines (They're all different sizes, so it's hard to mix them up, but mark them just in case) and remove the three bolts holding the plate in place (12mm IIRC), two on the head, one on the plenum. Don't forget to remove the two fat pipes attached to the ISCV too.
Now you'll be able to see the ISCV like so.
Step 2:
Now to remove the ISCV.
After you've disconnected the plug for the ISCV (and the other plug for the sensor that you will see is in your way) grab your Philips head screwdriver and remove the ISCV motor.
This will give you that little extra room needed to get a spanner in and pull the ISCV out.
Now, take a shortish 12mm ring spanner and remove the two bolts holding the ISCV on. It's a little tight, but it's in no way impossible.
Here's the result. A gaping hole (heh, gaping hole) in your engines nether regions.
Step 3.
Now, we have to open the thing up so it can have a good clean.
See the plate on the back of the ISCV? get a pen and put a mark on it to allow you to line it back up when it goes back together, then remove the two screws and pull the plate off.
You'll see the spring I'm talking about. This is the spring that looses it's springyness. I believe it's also a bimetallic strip, so as the engine heats up, the spring helps push the valve closed. This is the reason it's bolted to the engine, and also the reason we can't just relocate it to fix our problems.
Spring at the top, the plastic plug is the black thing at lower right.
Once you have it opened, you'll find a little plastic plug inside, which can be removed too. Note the orientation of the plug and the little lever inside, the lever normally points towards the engine block and the plug has three cutouts in the back, the lever fits into the middle sized one.
The correct orientation of that little lever for reassembly is up in this photo. (rotated 90deg anti-clockwise)
Now, you will be able to rotate the shaft 360 degrees. If you do so, and you can feel *any* resistance, you need to clean it.
Using your favourite degreaser, carby cleaner, etc. squirt it in while rotating the shaft back and forth until it's smoothly spinning. Give it a rinse to get the junk out and let it dry.
This is the bit to turn when cleaning.
Now for the spring adjustment. Fit it all back together, taking note to like the plate and spring up as per your mark. Just before you tighten the two screws, rotate the plate all the way anti-clockwise, then tighten the screws.
This will provide spring tension when the engine heats up to allow a bit of air through to keep your engine alive.
If you have the problem where your engine stalls when hot, this is most likely the fix.
If you want to, you can also check the resistance of the coils in the motor. Measure from the middle pin to each of the outside pins, they should read about 20-22 ohms, more importantly, they should be identical to within an ohm. if you measure between the two outer pins, it should read the same as both coils added together.
Step four.
Now to reinstall.
Basically it's a reversal of removing the thing. Be sure to put the motor on AFTER the ISCV is bolted in, or you won't be able to get the ring spanner in to tighten the bolts.
Once it's all back together, let the engine warm up until the fan comes on and see where your revs are sitting. Give it a few revs to see how it recovers from the sudden throttle closure (and 'cos ITB's sound sweet
). If it all seems good, go for a test drive and see how it goes. If the idle stays too high all the time (specifically when the engine is hot), then you'll have to turn that spring plate back a bit towards your original mark.Hope that helps, pics to come.
