IACV Setting - 0 Positioning
Turbo Mini Forums

Finally, I've got my head around setting up the IACV for my Turbo build.
Until now I have been having problems with the valve not always referencing to the same position each time the engine is started, so I’ve never been able to get a steady tick over from start up twice in a row.


I have worked through the megamanaul guide for the IACV setup - http://www.megamanual.com/ms2/IAC.htm

Although I have it working fine on the Clubman build, I could not work out why those setting would not work on the Turbo.
The main problem is that I have 2 different enclosures between the 2 builds – But the same model Peugeot IACV.

On the clubman I made an enclosure and the full range of movement for the pintle is 120 steps, for the Turbo build I am using an MPI enclosure and that gives a range of movement of 300 steps.

As I understand it, in order to have the pintle always move to the 0 position (fully open) at start up, the “start value” setting in Tunerstudio needs to be set to the max number of steps needed to fully close the valve, so in this case 300 Steps.

The problem (if it is actually a problem):
If the pintle is only at a position of 50 steps when the engine is shut down, the next time the engine is started the IACV will try to move back by 300 Steps So in this example 250 steps more than is necessary, hence what you get is the motor turning long after the pintle is a 0.

With the Clubman build, because the range is much less, the time the motor is trying to turn against an already closed pintle assembly is much less, so I had not really noticed the horrible noise the IACV makes trying to close when it is already closed.

The Question:
Will the fact that the motor is still trying to turn for a lot longer than it actually needs to at lower temperature start ups cause any damage to the IACV?


I’ve never pulled one apart, so I don’t know what is actually happening in there when the motor is either spinning or trying to spin against an already close pintle.

This will probably not always be the case as normally the engine will have been running long enough that the pintle is in is closed state (max steps)when the engine is shut down, but still , there will be a lot of times when it is not.

Thanks

Graham

’77 Clubman build thread
http://www.turbominis.co.uk/forums/index.php?p=vt&tid=618189

Siamese 5 port EFI testing
http://www.turbominis.co.uk/forums/index.php?p=vt&tid=611675

I have only set mine up on the bench using the stim, with the Peugeot valve and mpi body, but had the same problems. It doesn't remember where it last was so when cycling the ignition the initial open position varies.

I did the same as you and adjusted the settings such that it always bottoms outs. As you said the motor runs on a bit after it has bottomed out, but it then does go back to the correct starting position. I don't see a way around this, but also wondered if this will effect the life of the motor.

As you know, I use the Peugeot valve in an MPi body.

The only difference is that I've set the start value to 360. I don't have any odd noises and I get repeated steady tick-over on re-starts.

I think, and I emphasise the use of the word "think", that your perception of how it works is incorrect. The "start" value actually closes the valve before it opens to the position given in the idle steps table.

It's been a number of years since I set up my MS2, so I'm a bit vague. However I used the same setting on the MS3 last summer and did not get any problems.

If your valve is not fully closing with a start value of 300, then you could get the problems you describe, apart from the noise which is puzzling.

EDIT: The manual says that the start value is to fully open, but I remember a few years ago this was changed in the MS2/Extra code.

EDIT2: This is the MS3 manual which says what I thought and I'm pretty sure that the MS2/Extra code works the same:

http://www.msextra.com/doc/ms3/Idle_Control.html

Edited by Paul S on 9th Mar, 2012.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

I can pretty much backup what Paul is saying, as I was bench testing the Peugeot IAC valve and witnessed how the valve behaved on the MS2/Extra code, where the startup would open then valve right up (to the closed position when in a housing), and of course with it being out of the housing, the pintle would fly off across the room.

As for the strange noises you're getting, I've no idea where that's coming from as my valve opens all the way out, hits the MPi housing and then retracts to the number of steps according the coolant temp, but there is nothing audible as it hits the housing, it just stops the motor.

As above ^^^

When you first power up the MS2, the pintle should run "out" to close the valve and because it has to so this from any position it may have previously been in, the initial setting has to be greater than its potential travel.

This inevitably means the motor tries to carry on running when it has closed but they are stepper motors and designed to do exactly that - they draw very little extra current when held stationary and there are two current limiting resistors on the MS2 daughterboard.

Mine just makes a very light clicking sound for about 1sec after it is closed (while the motor is still trying to run), then drives back to the start position.

I set it all up on the bench, cable tied to a piece of wood with a screw mimicing the closed position so the pintle didn't fly across the room....

Two possibilities, either you haven't set the "start" value high enough to close it, or one of the pairs of wires is reversed on you second loom (which causes it to do the opposite of what it's supposed to). That's the other reason I set mine up on the bench, to work out which connection was which (mine's a Rover 800 valve and is unmarked for wiring).

Finally, are you waiting a couple of seconds when you turn the ignition on, before starting the engine - if not, it won't have time to wind all the way in, confirm zero, then wind out to the correct position.

Schrödinger's cat - so which one am I ???

I’m actually testing it on the JimStim at the moment. I removed the IACV and MPI enclosure from the engine to test.
I had wired it up to make it work as per http://www.megamanual.com/ms2/IAC.htm and http://www.msextra.com/doc/ms2extra/MS2-Ex...dware.htm#Fidle which both say the same thing (but worded differently):

Start Value (IACStart): The number of steps applied to retract the IAC pintle to 'wide open' at power up.
I’ve just change the set up to have the pintle full extend at startup (close the valve), then retract to the number of steps based on coolant temp. I Just reversed the coil wiring.
Now with a “start value” of 300, the IACV extends fully. Depending on the last position of the pintle at shut down I now get a short humming noise from the motor on next start up, better than the noise it made when it was trying to retract back pasts its fully open point.

’77 Clubman build thread
http://www.turbominis.co.uk/forums/index.php?p=vt&tid=618189

Siamese 5 port EFI testing
http://www.turbominis.co.uk/forums/index.php?p=vt&tid=611675