Well, you've found your problem then. This jives with you symtoms. With the idle air control valve out of action, you're idling on a fixed orifice. In this case, your idle speed will be lower at cold temperatures and higher when you're warmed up.

Next steps:
1. Monitor pins at idle air control valve for signal. You'll probably need a scope for this.
2. If signal present and correct, then swap idle air contol valve.
3. If signal not present, see if signal present at squirt pins.
4. If signal present at squirt pins, troubleshoot wiring.
5. If signal not present at squirt pins, time to dig into squirt.

If I had to guess, given that this is a newly built MS where this function has never worked, I'd say the problem is internal to the MS. Hopefully, you have the tools for this or a EE friend that can help. But at least you've solved the main part of the mystery and you are no longer changing MS parameters and scratching your head.

I just reread your original post, and it seems you've already confirmed a good idle air control valve.

When you did the following:

"2. Changed the polarity of the Diode on the 2 wires on the Idle valve to see if I had fitted it wrong."

you could easily have damaged something. If this diode goes across the solenoid wires, then it is there to allow high voltages that result from the breakdown of the magnetic field in the solenoid winding to dissipate (think ignition coil -- all coils, such as those in the solenoid of the idle air control valve, produce these voltages). By reversing or removing the diode, you forced that voltage to dissipate through the electronics of the MS.

Thanks for the replies bud, I have the iac diode between the 2 wires at the iac connector, I think we are thinking the same thing. would the diode have been damaged or something more serious in the MS?
Barry

It would be something more serious. The usual failure mode for a diode is open -- so it shouldn't knock your iac valve out of action even if it is blown. Easy to tell with a multimeter.

However, you mentioned having the symptoms even before you touched the diode. So, something would have been wrong prior, and is still probably wrong now. Given that your iac valve has always been non-responsive, there may not be any further damage from the diode experiment. We can hope, right?

Anyway, you've exhausted my EE knowledge. Probably time to engage some of the more knowledgeable types like Matt or Brain.

Bud, just like to say a big thank you for your time:beer: Appreciated...
Barry

I may see if I can buy the IAC component pack for the ms and renew those parts to see if that works...

Have you checked to see if the "air valve" on the manifold is operating correctly? Water going thru? gaskets ok?

I have recently change the inlet manifold and renewed all of the gaskets so it should be OK.

Uhhhhhh . . . the Air Valve that Older Guy is talking about is an active mechanical component. Simply renewing gaskets is not a guarantee that it is working. It could very well be stuck.

I recommend the following website to help you understand the idle mechanisms on your engine:

http://www.miata.net/garage/isc.html

It will help you, I promise.

Could someone have a quick look at the photos to see if any obvious idle mod issues are evident, many thanks
Barry

Is the R39 jumper in place? The wires are in the way but it almost looks like it's missing.

Hi Matt,
Following the instructions here http://www.megamanual.com/index.html

It says: Do not install Q20, do not install D8, and jumper R39 as well, I may have read that as 'do not jumper R39', I will need to whip out my MS and confirm if I have done it or not.

Could this be my problem?
Barry

You have the thing programmed for the Southern Hemisphere! Just click Northern and all will be well.

Found another image, I did jump R39....
Barry

I take it that was an 'attempt' at humour!!.......:giggle:

I have the 1N4001 diode across the 2 wires that go to the idle valve connector, is that correct?