ISCV/IACV 20v BT; Running poor

[NoisyBoy]

Hey guys, im in the middle of trying to diagnose some strange isses with my 20v Blacktop, that have started to get worse over the passed two months. Im trying to find a tech write up on how the ISCV/IACV (Idle air control valve) should function in ideal scenario's. Once warmed up should it close and stay closed until the next time its cold again? Does it pop back open when you idle but are at running tempurature? My TOYOBD1 seems to show it is constantly functioning, always adjusting at all times. Comparatively a 3VZ shows once warm, the IACV is no longer active, it settles at a constant value, which appears to be closed, and does not change until the engine is turned off.

My issue is mild bogging if VVT is left active (i have a switch to force it off, it runs a little better without) upon rev matching or rev falling between gear shifts there is a pop/spat/backfire, it is louder than normal, is certainly down on power, idle mostly dips down below 1000rpm, but often when just started in the cold (often 0 degrees C now) the idle goes high to 2000rpm+, and revs fall and it goes back up, it happens rather quickly and will re-occur two or three times. This seems to be worse the colder it gets, for example if i have the rad fan on before the car has started.
Ive got a list of things to diagnose, (MAP, throttles, IACV, TPS, intake air temp sensor, ignition system... etc). This engine has run very healthy through 60000km in my own hands, and only recently has this started.

Any and all help, including links to threads to read, is really appreciated.

Thanks Corolla people,
love you

[jondee86]

All the idle air for your BT engine passes thru the ISCV. The ECU monitors the
engine rpm and modulates the ISCV to hold the target 880rpm idle speed steady
against various load factors. It also operates to raise the idle to assist starting,
and prevent stalling by quickly adding extra air when the idle rpm dips.

It is my understanding (not confirmed by hard facts) that the ISCV is only active
while the engine is idling. I would guess that once the engine is driving with the
throttles open (IDL switch open) the ISCV will remain in the position it was at
when the IDL switch changed state. It will become active when the IDL switch
closes again indicating that the engine is idling.

The ECU will apply corrections to the ignition timing and fuel mixture to improve
idle quality, so it is important to ensure that the TPS is correctly adjusted. Don't
know if this helps, but it's all I got

Cheers... jondee86

[NoisyBoy]

Thanks Johndee86, that was actually quite helpful, i was under the impression it should stop functioning. On an old forum post someone had said that if you put 12v to the center pin of ISCV and ground to left or right pin, it should have a defined click sound, not a soft one. It clicks, how defined or soft hard to say, but it appears to make a constant clicking sound as long as it has power on either side.
Small update, my idle is actually normally around 1100rpm when warm. Today i checked and tested a few things, swapped air temp sensor for a spare i had, and my spark plugs had white ashy deposits on them, as well as the gap being quite large, so i changed them for a new set of NGK BKR6IEX11. While it may have improved the problem is still there.
Next tests on the list to check intake/trumpets for combustion leaks, TPS and MAP sensor. Asside from that im starting to question if the timing has gone out a bit.

Any and all help is appreciated, as an engineering student, diagnosis time for the 4AGE daily is really really limited.
Thanks guys,
NoisyBoy

[jondee86]

The ISCV is a rotary PWM solenoid valve with two coils (RSC and RSO).
Both coils are energised by the ECU supplying a PWM ground when the engine
is idling. The PWM signals are inverted, so that as the voltage on one coil
increases, the other reduces. A spring is incorporated into the base of the
valve to return the valve to a safe idle in the event that the ECU signals fail.

So yes, applying 12V to either coil as you describe will result in a single metallic
click as the solenoid hits the stop in one direction or the other. There should
not be any continuous clicking if a steady 12V is applied. It is not unusual for
the ISCV to get a buildup of black crud (technical term) inside that can cause
the valve to become sticky/stuck/erratic. Standard cure is to remove the valve
and flush it out thru the inlet and outlet tubes with carb cleaner spray. A clean
valve will make a clear metallic click when energised with 12V.

Cheers... jondee86

[NoisyBoy]

Thanks for saving the day again! I had planned to clean it out, but its good to know somebody else understood what i meant. On another note, im suspecting timing as a culprit here, and noticed that my igintion timing (the slider on the distributor) is fully (if not almost fully) clockwise, this would be fully advanced would it not? This would also most likely be problematic on a stock 20v BT? I can get a timing light, but for temporary problem solving, if i were to set the distributor in the middle position for a more neutral timing setting, does the engine need to be running with the diagnostic pin shorted for me to adjust it?

Thanks
NoisyBoy

[jondee86]

does the engine need to be running with the diagnostic pin shorted for me to adjust it?

No, you can adjust it without being in diagnostic mode or with a timing light... you
just won't know what timing you actually have Turn it and see what difference (if any)
it makes. Listen carefully for any sign of knocking when you apply a lot of throttle at low
rpm in a high gear. If you hear knock (pinking) then go back towards where it was before.

Cheers... jondee86