I've got a OBDII 1.8 its a bit different. No coolant through IAC = no idle when hot = ECU throwing idle control codes = no pass emissions. I could do what Jman suggests, but its not worth it to me to swap IACs every time.

What's the air valve do? [/n00b]

It controls the idle mixture by leaking a controlled amount of air into the intake manifold.
DO A SEARCH! :)

http://www.boostedmiata.com/random/idle_passages.jpg

it's designed for cold starts only.

when cold it allows air to bypass the TB and enter directly into the intake manifold for a smoother idle. it also at the same time heats the air as the coolant passes through the ISC valve. Once a certain temp is achieved (70°F), the spring in the air valve closes and then it sits and does nothing.

Seeing as how multi-cylinder motorcycles dont have anything for idle control, and they still do idle pretty decently (that too on a crazy cam with ITB's), I'm wondering how important the IAC valve is on a performance-oriented vehicle.

Anyone disconnected the IAC valve? Or not controlling one on their MS setup? It would make the coldside piping SO much more easier.

EDIT: I just realized you can add a small air filter to the IAC hose instead of hooking it up to the coldside piping. Specially if you have a MAP sensor.

can you just remove that whole block from underneath the throttle body?

Thanks Brain! Good explanation.

ZX - I've been here a good deal longer than you (not that that makes me better, just sayin') and never seen the air valve mentioned before.

no cause you need the idle valve to idle below 1200RPM :)

oh ok thanks. but you can remove the air valve, block it off, then block off the other coolant hoses that lead to it.

Sorry, no offense intended :)

Same thing you call air valve - there is some wax in it which expands from the hot coolant.

On a NA8 it is part of the ISC and you can't just unbolt it like on a NA6. You have to unbolt the ISC, pour some gasket maker in wax valve's air channels (but be careful not to plug the idle solenoid) and leave it for few days to dry out. If one doesn't do this but just disconnects the coolant lines from the NA8 throttle body, he ends up with quite a random idle gremlins depending on things like the ambient air temp ...

Oh you've got to be kidding me.

I pulled the coolant lines on my NA8 forever and a day ago, it's had some funky idle issues (mainly whenever i hit the brake). All I did was pull the lines and cap the holes. Any guidance on what passages i need to block on my NA8? This is the first I've ever heard of such a thing; all the passages looked like there was nothing to worry about in them.

Take it apart and you'll figure it out. It is clearly seen which passages are for the vax valve and which for the idle solenoid. Also you can check how much air goes through before removing the IAC because when disconnected the solenoid is shut - all that flow you're getting is through the wax valve

Isn't it the opposite way around? I removed mine, and now it idles around 900 when cold. When it warms up, idles around 1600. I would think that it works like a choke (less air when cold = richer mixture) where once it warms up (ie:coolant temp increases), air valve opens to allow more air in through that extra channel?

Although, in my scenario, it doesn't make sense why my idle jumps up since I'm not using the air valve or the IAC. Idle is controlled with the TEC3 -- I need to play with the maps so warm idle doesn't go crazy like that.

what am i supposed to do about idle once i remove my stock tb for this 70mm one with no iac? something i can do with the MS?

http://www.miatamx5.com/begiturbomani/tb-2.jpg

With most standalones you can control the idle with ignition timing rather than an ISC.
I can't speak for MS, but my DSM runs an Autronic SMC and the ISC is removed with the passages blocked. I want it to idle at 1000RPM, so I set the idle ignition timing (when TPS is less than 2%) to 25deg at 850, and 0deg at 1100. Then adjust the throttle stop (or the idle air screw) until it idles at 1000 with 1 or 2 degrees of advance. When it's cold I have to hold open the throttle for a couple minutes until it gets some heat into the motor or it'll die. After that it's fine. You'll probably have to play with the fueling a bit to get a smooth idle at 0deg advance.

What happens to the EGT at that point? Does it go high enough to do any damage?

EGT at idle is fine, around 900F.

Even WITH the ISC, my miata idles at ~5deg so I can have the throttle-plate open as far as possible for anti-lag use. Same story there, less than 1000F idle. However if you kick on the ALS (-30deg advance), it'll peg the EGT gauge if you don't watch it :eek5:

I have it plugged just like braineack is doing and I passed california state emmissions on the oem ecu. The main problem is it wants to idle very low when the car is cold, so i backed out the screw a few turns until the car was warm.

Ok, so, since I removed and plate my IAC, the air valve is useless, so I can just caped it?

right?

Sorry for digging up old post, but this is searching instead of new posting!