IAC Valve (Miata Content)

I am having trouble with my 1994 Miata's IAC valve. It's the 1.8 engine, but you knew that. I finally took it apart and here's what I found.

1.) There is 0 Ohms of resistance on the valve. I understand that it should be between 10.3 and 12.5 or something. This could be cause for concern, but the meter might be broken too.

2.) The device still activates and deactivates. The problem is that the car idles way too fast when the IAC is plugged in. It's like it's opened at least partially all the time when it has power. Unplugging it fixes the idle problem but I cannot use the AC while I'm sitting still.

3.) I cannot, for the life of me, figure out HOW THE HELL THIS THING WORKS! It has coolant lines running to and from it. The coolant seems to flow through chambers in the device. Is this just to keep the incoming air cool or does it actually provide some means of operating the unit? I heard the RX-8s have liquid cooled throttle bodies. Is this what I am seeing?

Also, does anybody know why these cost between $500 and $800? Does anyone know where I can get one for less? Maybe, you know, $80.00?

Any input is appreciated. Thanks!

Dang. I thought the whole cars sold for $500-800. Maybe buy another one, take the IAC out, ebay the rest, Profit! Or, strip the rest down, save the pieces for your Locost project that you'll MegaSquirt with a Chevy IAC anyway, sell the rest, Break Even and get a Locost.

I'm no Miata expert, but I saw one once. If it works like a Toyota, the coolant lines will make the IAC give the motor more air when the motor is cold. Toyota used a wax pellet or something in theirs. After it is warmed up, then the electrical aspects come into play. Get a better meter, or one you have confidence in, or learn the one you have. Set it at the lowest resistance scale and check the valve again. If you have it set on 20K Ohms max scale, then it will likely show 0 Ohms resistance. If you have it set at 200 Ohms max scale, you will see the correct reading.

Google is my friend.

http://raleigh.craigslist.org/pts/824608422.html

also, it appears that you can use one from a protege.

http://forum.miata.net/vb/printthread.php?t=265594

planetmiata.com will likely have them.

YOU GUYS ARE HEROS!

Techron fixed mine up!

Rogue wrote: Techron fixed mine up!

What did you do with it? How do you use it in the IAC?

It is added to the fuel.

I now run a bottle just prior to oil change.

I now suspect a vacuum leak. The car idles irratically. The iac IS doing something. The car idles OK while it is just sitting. But when you turn on the ac or turn the wheel the car overreacts and the idle jumps to 2,000 or 3,000 rpms. Then it bounces between 1,500 and 2,000 quickly for a while. Grrr.

Does anybody have any ideas? I just unplugged it (the iac) and it seems fine again. But it is idling a tad higher Than it used to while unplugged. I'm out of ideas.

Okey doke. Did you turn the throttle valve stop screw while trying to run the problem down? If so, that will cause exactly what you are describing. That's why a lot of techs call it the 'don't touch it' screw. Those things are set on a flow bench type thing, it's a metered air leak past the throttle valve.

Assuming it's been tweaked, try this: back the screw all the way out until it no longer touches the lever. Then, turn it back in until it touches, then turn an additional 1/2 turn. See if the idle gets better, remember the ECU has to relearn the idle so it might not be OK right away. If it gets better but still is a bit erratic, try an additional 1/4 turn.

I didn't touch that. It seems to be covered in some sort of glue too, so I am certain that it hasn't moved. I think it's probably a vacuum leak. Could that be possible? Maybe air is sneaking in through a vacuum hose and past the throttle?

I'm stumped. Stupid idle issues.

OK. I'm going to go touch the "don't touch it" screw. I'll keep track of how far I move it (not much) and reset it if it doesn't solve the problem. It appears as if the glue had come off recently and the screw looks like it moves somewhat freely. Maybe it vibrated out of the correct setting?

sory this is an old topic, but maybe someone else will benefit from this post. The IAC can not be cleaned with techron... its the air intake and is on the outside of your throttle body. If you have enough techron fuel residue blowing back through your throttle body to clean your IAC then you better figgure out why you have positive pressure on your intake manifold... Maybe Rogue was refereing to an Idle problem and not the actual IAC valve.

The IAC is controled by the ECU and pulses to the IAC's solenoid coil control how much it opens and when. When you activate the brakes, or turn on the A.C. or turn on your headlights, or turn the steering wheel with power steering, there is an aditional load on the engine from either the alternator or the A.C. compressor or the powersteering pump. The IAC is then open or closed to the appropriate aperature to compensate for the extra load on the engine. If the Idle is fluxuating, then your IAC solenoid and ECU are probably working fine. They are switching the IAC valve to compensate for extra load on the engine, but the vavle on the IAC is probably sticking and delaying the reaction time, causing surging and loping at idle. If it's gummed up it can be cleaned with carb cleaner and it will save from having to purchase a new one.
Some causes for the IAC to gum up are running a dirty filter, or using an aftermarket Oiled filter that most CAI kits come with.

As far as adjusting the Idle, theres an idle adjustment screw under a rubber cap on your throttle body. You have to jumper pins 10 and ground on the diagnostic connector under the hood, then you can adjust your idle speed using this screw. Don't mess with the throttle position screw on the throttle linkage.

Just a small clarification, you should jumper pins TEN to GND on the diagnostic connector next to the air box.