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Miata turbo IACV

Old 05-02-2019, 09:40 AM
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Default Miata turbo IACV


I was just wondering how you guys hook up your IAC valves, I have not managed to find anything relevant at the forums except this picture which people seem to have very different opinions about.

My Idle is currently very lean (19.9 AFR) and im wondering if this is the reason. If not please point me in the right direction.


Last edited by Davinci; 05-02-2019 at 09:43 AM. Reason: Picture removed text
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Old 05-02-2019, 06:20 PM
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Seems fine to me. That's basically the same as how the FM intake pipe is set up:

In the FM intake, the hose branch on the right (as pictured) goes to the IACV (the same as the 3/8 hose in your picture), the branch on the left is for the BOV, center goes on the TB. I've seen some cars with a stand-alone mini air filter hooked up on the IACV, which I think should also be fine with a MS or other system using MAP rather than air volume through an upstream MAF, which the stand-alone filter would bypass. If you're using the stock computer at idle, you would want to keep the IACV plumbed in where it will draw air through the intake downstream of the MAF.
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Old 05-02-2019, 06:53 PM
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You'll want to bypass a lot more air volume than that I would think, otherwise you'll have a very narrow band of RPM you can control, and you may run into the issue of not having enough even at 100% DC to idle when cold.

Beyond that, your IAC controls your RPM, not your afr. If it let more air in, it would idle high, not just lean. You either have an exhaust leak near your o2 that's sucking in air at idle (very common), or your wideband is miscalibrated. You're not idling at 19.9, your engine would stall.
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