M20B25 ICV Operation

[Eddie1990]

Hi,

This seems like a daft question, but how does the ICV work on the M20B25?

I know it allows a preset amount of air through it, but how?

The little "door" inside, does it rotate? I checked mine the other day, and when the key is on ignition, the ICV buzzes, but the "door" doesn't move. I can move it with a screwdriver, and it just goes back to where it was. I was under the impression that the door rotated inside the valve, but I can't find a definitive answer.

Any advice would be greatly appreciated.

[jslot]

Yeah it rotates inside. There is effectively 2 coils inside that fight each other, one trying to open it, the other trying to close it. The ECU sends varying voltage (I think) to each to control how much it is open, to control the idle rpm, when the throttle position switch indicates closed throttle.

I think you can put 12v to the middle terminal, and either outer terminal and it should snap open/closed.

[Eddie1990]

Yeah, I know it snaps shut, but does it just stay shut or should it move open and closed?

Mine is snapping shut and staying there, and I'm having issues with idling/stalling.

The valve itself moves freely and I've cleaned it out plenty of times, but the valve only rotates about 180 degrees, not a full 360, is that right?

[jslot]

If the ignition is on and its idling it should be open a little bit. If it isnt opening at all when it should ( when car is being asked to idle), then something is wrong.

[jslot]

just checked what my ICV does as I was curious.

Key out of ignition - fully shut.
Key turned to ignition on but engine not on - fully shut but buzzing.
Key turned to engage the starter motor - open (fully open I think).
(then the egine should start and the ICV will modulate to control the rpm, until you press throttle then you control rpm with your foot!)

If your ICV will open when it should then your problem might be elsewhere. Even if your ICV wont open at all, the ICV might be fine, but you may have a faulty ECU (a certain age of ECUs can develop a fault in their idle control circuitry), or even the ECU doesn't think the throttle is closed so won't even attempt to engage the ICV.

Double check the TPS. You can rule it our by bridging the appropriate pins on the connector (can't remember if left and centre or right and centre) to ensure 100% that the ECU is seeing the throttle closed signal, and therefore telling the ICV to operate. As far as I am aware ICV will be totally closed unless the TPS is signalling throttle closed.

From your other thread you mentioned it can be fine when cold but bad when warm?

I only feel confident answering questions about idle problems cause I think I have had them all in the past.

One of the faults I developed would be stalling on idle when engine was hot. It turned out to be a dry solder joint on the throttle closed microswitch in the TPS, that must have made a decent electrical connection until everything got hot. I had been scratching my head because the TPS would check out fine with a multimeter.

[jslot]

ICV doesn't rotate that much at all, probably less than 180 degrees.

[Eddie1990]

Thanks for the advice, yeah it's tricky finding faults that are intermittent.

I'll do some checking tonight.