ICV Operation

[SVBMW]

I know that the ECU takes over control of the engine as soon as the butterfly/TPS moves but when does the ICV "let go"?

For example, if when you let the cluch in the revs drop, is the engine speed maintained by the ICV or the AFM??

Cheers

Tris

[Brianmoooore]

Don't think the ICV ever 'lets go'. If the revs drop below 750 or whatever is programmed into the ECU, the ECU opens the ICV to try to raise the revs.

[Simon]

When you say let go..do you mean stop functioning??

The ICV is only really in operation when the butterfly is closed, it bypasses the butterfly to keep the idle flat as Brian says.

[Brianmoooore]

For instance, if you try to climb a steep hill in top gear, you will lose speed and engine revs and eventualy they will dip below 750 RPM. At this point I would expect that the ICV opens fully, but since this small orrifice is in parallel with the wide open throttle in the throttle body, it's not going to make much difference to total airflow.

[Andy335Touring]

I'd have thought that the ICV will only open with a closed throttle ?

[Brianmoooore]

You might be right Andy, but the point is, with the throttle open, it's not going to make any significant difference what the ICV does.

[SVBMW]

Thanks for your thoughts chaps, thats exactly the dilema I had!

Still I've bitten the bulet and orderd a new one at Ԛ£72 +VAT

I'll post the outcome later

Tris

[SVBMW]

Fitted it and now have a nice smooth idle with no hunting, even from cold.

The puzzling thing is though that at no stage could I find a suspicion of anything being wrong with the old one, mechanically or electrically.

tris

[Brianmoooore]

I had one fail suddenly about three months ago, the only non wearing part I've ever had fail for no apparent reason on any of my cars.
Couldn't find anything wrong with the old one either, but a new one cured the problem. Put the old one back, problem reapeared.
Even stranger, the symptoms were, that running on petrol I had a slightly increased idle speed, but on LPG it constantly revved to about 2500 RPM then cut and only just caught again as it was about to stall, then up to 2500 again and so on. The idle valve works in exactly the same way on petrol as on LPG, and I can think of no reason whatsoever why I should have such dramatically different symptoms.

[MarkP]

Recently I have noticed that my sport sits around the 2500RPM when started from cold. Sounds like the problem is this ICV, is there anything I can do to it apart from replace it with a new one?