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julianfoulger wrote: wrote:

Thanks for that.

This is good sum-up from David Aiketgate

David Aiketgate wrote: wrote:

Resetting the iacv (stepper motor) merely tells the ecu that the throttle butterfly is at 3.9% open.(Don't quote me on the actual figure)
If your throttle is actually a way off 3.9% open, the IACV is confused and varies between step settings trying to achieve the correct idle.
Hence the idle rising and falling, or being way too high..

This is complicated because the stepper motor/IACV actually does have stepped settings and the ecu will try to get you to one of the steps. Step 21, I believe.

If your base idle is wrong then this is an endless loop of the ecu using the stepper settings to try to get a set of correct readings.

If you vaguely followed that, what you need to do is get the engine fully up to temperature after a good blast, come home let it idle, but disconnect the IACV plug. Let the idle settle for a few minutes and use torque app or pscan to see what the base idle is. It should be 850-875rpm. (Assuming no other reason ie vac leak, sensor problem.)
If the idle is substantially above or below this then the stepper motor/iacv will constantly hunt or fail to get the idle correct.

You need to adjust the idle set screw on the throttle body.
(I know there are a lot of people who say you must not alter this as it's factory set, but it is adjustable. Its just that the manufacturer didn't want amateurs fiddling with it, hence the non tamper cover that might still be in place) Adjustment may be necessary over time due to wear, or especially if the throttle body has been swapped.

So, reset the base idle to 850 using the set screw on the throttle body, no more than 1/4 turn at a time. After each adjustment wait until the idle settles. Once you've got reasonably close, reconnect the IACV and see what happens for about 5 minutes. If the idle settles to a stable level near 875, great!
If not then you'll need to adjust the idle screw a small amount until you achieve a stable idle somewhere between 850-890rpm. Sometimes you might think you are nearly there and the idle will suddenly change. This is the ecu making the stepper motor move to the next step. Hopefully you will be on step 21 already but if not you'll have to keep adjusting, until you achieve 875 and step 21..

Once you are happy switch off and reset the TPS, if you still have the torque/ pscan connected you'll see the tps sensor change to 3.9% from whatever it was.

I went through all this a couple of years ago and the idle has been rock solid since.
David

Best explanation that I have seen. Thks.

The standard data for idle that I have is throttle opening 4 degrees (agrees with the above), idle revs 875 rpm (we agree) but a step range between 20 and 40 steps. David is suggesting it should be on step 21 - I would suggest that it should be the middle of the range ie 30 steps. I am not saying that he is wrong; just curious as to the difference.....

julianfoulger wrote: wrote:

Best explanation that I have seen. Thks.

The standard data for idle that I have is throttle opening 4 degrees (agrees with the above), idle revs 875 rpm (we agree) but a step range between 20 and 40 steps. David is suggesting it should be on step 21 - I would suggest that it should be the middle of the range ie 30 steps. I am not saying that he is wrong; just curious as to the difference.....

Step 21 is the correct. When mine was set up you could noticeably hear the difference as the screw was adjusted.
Marina Brian who kindly set mine up on T4, virtually speaks K Series lol he’s a very very knowledgable bloke


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Thanks for the comments. I shall use 21 as the target now!

julianfoulger wrote: wrote:

Thanks for the comments. I shall use 21 as the target now!

How did you get on


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Stepper running at 21 steps and RPM of 875 when water and oil fully hot. Appears to be rock steady but I have yet to go on a decent run to fully test. I marked the original position of the idle screw; I had to move it 1/2 turn clockwise (from the position when bought 15 years ago) to get it down from 55-60 steps to 21 steps which, to my mind, is a lot.

julianfoulger wrote: wrote:

Stepper running at 21 steps and RPM of 875 when water and oil fully hot. Appears to be rock steady but I have yet to go on a decent run to fully test. I marked the original position of the idle screw; I had to move it 1/2 turn clockwise (from the position when bought 15 years ago) to get it down from 55-60 steps to 21 steps which, to my mind, is a lot.

Mine was 83 lol, it hadn’t been touched since leaving longbridge lol.


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One kind of wonders whether it was ever right....... As an aside, Pscan says that 25-27 is the correct setting. When you get below 25 steps Pscan says turn the screw anti-clockwise to increase the steps.

Interestingly, there is relatively very little on the Web about what to adjust the stepper to outside the Pscan forum.

julianfoulger wrote: wrote:

One kind of wonders whether it was ever right....... As an aside, Pscan says that 25-27 is the correct setting. When you get below 25 steps Pscan says turn the screw anti-clockwise to increase the steps.

Interestingly, there is relatively very little on the Web about what to adjust the stepper to outside the Pscan forum.

That’s strange 21 is the figure on T4 lol I’m definitely going to invest in PScan though. It’s seems will do everything I need


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I thought I was there regarding a steady idle (875rpm, step 21) until I went for a spin today. After 15 minutes the steady idle I had was up to 1688rpm (albeit steady). Turn-off and then restarted - it adjusts back to circa 875rpm.

I got home, and following the advice above to the letter, disconnected the IACV and then adjusted the screw (both ways) but the RPM stayed on circa 1050rpm. I just do not seem to be able to get it down to 875rpm. Any thoughts?

On Pscan I get no error codes (other than the IACV because disconnected), I have already replaced the spark leads, coils, TPS, cam sensor, MAP (and the IACV). The throttle cable is as to should be (ie no pull on the cable when peddle not pressed).

Any ideas, please?

julianfoulger wrote: wrote:

I thought I was there regarding a steady idle (875rpm, step 21) until I went for a spin today. After 15 minutes the steady idle I had was up to 1688rpm (albeit steady). Turn-off and then restarted - it adjusts back to circa 875rpm.

I got home, and following the advice above to the letter, disconnected the IACV and then adjusted the screw (both ways) but the RPM stayed on circa 1050rpm. I just do not seem to be able to get it down to 875rpm. Any thoughts?

On Pscan I get no error codes (other than the IACV because disconnected), I have already replaced the spark leads, coils, TPS, cam sensor, MAP (and the IACV). The throttle cable is as to should be (ie no pull on the cable when peddle not pressed).

Any ideas, please?

We just adjusted the screw on mine didn’t disconnect the IACV


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Air leak or warped throttle body?