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Old 01-05-2015, 02:37 PM   #1
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Default Fast Idle Issue

It's been cold so i've been procrastinating.... and Holidays so I've had plenty to do elsewhere anyway...

A few weeks ago on my way home my idle went crazy about a mile from home. So now I'm idling at 2k+. The idle was fine until that day and has been crazy since.

In the past I've had vacuum leaks in such places as injector seals, dried or cracked out vacuum plugs, etc...

I was unable to locate a leak so started messing with other stuff.

oh yeah my motor is a 99 on ms3. I Just got my idle dialed in i thought about 2 months ago and was a happy camper.

Anyway.... It doesn't matter if my motor is warm or cold it still idles like a bat out of hell.

Things that stick out in my troubleshooting are.

1) with the idle screw all the way in my idle is still 2k
2) if i unplug my iac my car does not die (even if it's 35 degrees out and a cold start). If the idle changes at all it's not really enough to note. Maybe 100rpm

3) I was unable to locate a vacuum leak anywhere on the IM.

4) If I create a leak via unplugging my map sensor I idle relatively normal with a little surge.

So i've searched a bit about IAC's and fast idle but have not really gleaned any helpful information.

Any thoughts? I'm just throwing this out there so any bored or knowledgeable people can shed some light on possibilities. Again I haven't put a ton of effort into anything yet but will attempt to figure it out later tonight.


Edit:
found this: https://www.miataturbo.net/megasquir...2-steps-79194/

Any other thought meanwhile are appreciated.

Last edited by krissetsfire; 01-05-2015 at 02:49 PM.
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Old 01-05-2015, 02:58 PM   #2
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I appear to have d4 still in from when I upgraded from ms1 to 3. Is this still valid?
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Old 01-05-2015, 03:44 PM   #3
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I must be really unlucky or have built this thing way wrong. 2nd time I've had corrupted firmware. Re flashed and it's back to normal.
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Old 03-22-2015, 01:25 AM   #4
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must have been coincidental because the fast idle is back. I put a smoke tester on my IM and the only place i saw smoke coming out was the tb. Is it possible I have a bad IAC? Anyone had a bad IAC cause a fast idle?

All of the 1st post still applies. idle screw is in completely.

Last edited by krissetsfire; 03-22-2015 at 01:49 AM.
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Old 04-05-2015, 09:58 PM   #5
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solved: iac solenoid stuck partially open. couldnt get it to reliably close after forcing it shut. replaced iac. car works fine now.

i injected smoke into my manifold and it only came out the throttle body. vacuum leak isolated to tb.
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