Good you found that problem :-)

It is likely that the ISV disconnected itself when the engine was at normal operating temp. So the setting would be close for normal running temps. The ST2 indicates the measure of the signal applied to the ISV. That figure of course uses the feedback idle loop and adaptation values that the LH computes are necessary.

It could well explain the reluctance to idle when cold, although your ambient "Cold" temp is high, which would explain why the car would quickly get to the point where it would idle from cold.

 

John,

The thing that threw me was that the idle was finding a stable setting. I understood that if the idle connection was disconnected then there would be no idle any time yet alone so close to correct. Does this mean the ISV naturally settles somewhere in the middle as a default and then opens/closes as a function of rpm variance?

Anyway I learnt that if the idle value in ST2 is next to nothing then that is the sign of a disconnect.

On the positive side, the car is clearly firing during cranking now and I am confident it will fire up well when "cold". Again today the engine temp before firing anything up was 31C and indeed it very quickly warms up to 50C and then continues onwards and upwards.

It will be interesting to experiment a little more pulling back the CPW until it seems to struggle to start.

Regards

Fred

 

Fred, glad you found it.

With zero volts the ISV is partially open as a "fail safe" value which allows the engine to idle, although not with any stability-- as you noted. The "closed" ISV value is around 30-35%, and at zero it partially opens again. So when there is a fault, or the ISV is disconnected, there is enough idle air to run the engine.

I'll send an email with the injector-size tests, I am working on documentation for that.

Cheers, Jim

 

Jim,

I sure felt a bit on the dumb side when I realised what the problem probably was. Happy to share my setting when I finish them- main thing is I do not want to overcook them and end up with something that is a pig to start when hot.

Regards

fred

 

When I had my S4 intake off, I was struck by the smarter design of the LH 2.3 IAC/ICV vs. the LH 2.2 unit, which requires a separate bypass air source (TB screw).

When the LH 2.3 ICV flapper is in the unpowered, uncycled, (spring loaded) closed position, there is a ~2mm gap. (I think this translates to around 1000 rpm.)

Up to about 1/3(?) rotation, the valve is fully closed.

In the fully rotated, open position, the valve is completely open. (Enough air for up to ~2000 rpm when warm.)

 

Ken,

When the motor is warmed up I saw a tickover of about 800 rpm with the a/c switched off and it dropped to about a normal 680 with the a/c. I rarely run without the a/c thus did not notice the difference [initially]. Seems like quite a well thought out set up.

Regards

Fred