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Discussion Starter · #1 ·
So lately this has gotten worse. My idle dip issue persists after adjusting the idle screw and bridging 10 and ground. But also recently my idle will intermittently go to 1500-2000 rpm and stay for 30 seconds or so then settle back down. I have also noticed the engine will keep revving 200 rpm or so after i take my foot of the gas during a shift. It seems to have a rough time with cold starts and smells pretty rich. On cold starts it will sometimes die because of the idle dip.

Can anyone help me out? thanks.
 

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did you mess with the thing on the side of the throttle body? I don't know what its called but it has a adjustment on it and if its not right it will cause weird things to happen.
 

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And what may this thing be?

My roommate is having these problems on his 1.6.
 

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The Idle Air Control Valve? It may need to be cleaned. I had a similar problem on my Integra.
 

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the stupid damper screw thingy(throttle idle stop) if its to high it makes your idle go down really slow
adjust this thing, if not look for a vacuum leak
would post pics but you didnt post what year your car is

(edit)
 

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also check your timing with a timing light and paperclip on ten to grd , then adjust your cas, maybe ur timing is advanced?
 

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the stupid damper screw thingy(throttle idle stop) if its to high it makes your idle go down really slow
adjust this thing, if not look for a vacuum leak
would post pics but you didnt post what year your car is

(edit)
How exactly do you adjust this? Like which way makes the idle fall down
 

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I think Bronto is right, it sounds like a gummy ISC.

Try disconnecting the electrical connection on it to see if idle changes (should go to high idle by default).

Check the wires on the ISC connector (engine harness side - female) to see if the two wires are exposed, touching, corroded, or damaged.

Clean the connector with electrical connector clean and plug it back in and fire up the car.

If that doesn't fix it you will probably have to clean the ISC.

You will have to remove the throttle body to get at it. The screws that attach it to the TB are REALLY soft, so use a pair of vice grips on the screw head WITH a phillips screw driver and turn them both at the same time to get them loose. There is a sensitive "gland" valve between the TB and the ISC, so be gentle when you separate them.

Only clean the ISC with electrical cleaner or throttle body cleaner. Other cleaners, like carb cleaner, is too harsh and will most likely ruin it. use some q-tips and pic tools to clean out the crevices. Might as do the same with the TB while it's off.
 

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KFJ FOR PRESIDENT.

For real, that fixed it. The SC confused us and we didn't know that was indeed the ISC.
 

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Glad to help!

FWIW, those ISCs on the 1.6 are problematic as they age. They are the kind of part I look for in part-out ads, junk yards, or Miata swap meets. Brand new, they are $400+.
 

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Totally hijacking but its my first offense so let it go. :blaugh:
I just cleaned my IM and TB on my '00 and after putting it back together the car idled like this, it'll idle up high and then droop like his. Y'all think I have the same issue and fix?
Also definitely no vacuum leaks.
 

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If the problem is the isc and cleaning it doesn't help can I drive without it plugged in until I bought a different one.
 

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Discussion Starter · #17 ·

So during the 12 days this thread was DOA, I removed the air pipe hose connecting the ISC to the manifold and sprayed like half a can of carb cleaner into it while the engine was running. I hope it doesnt end up ruining the ISC, but so far it has helped quite significantly. I still have a smidgen of dip, maybe 100-200 rpm, but it is few and far between. Since I have done this and changed the oil to m1 0w-40 it has never dipped or died when cold. So as KFJ and bronto suspected, I am quite sure the ISC is my problem, I will probably remove it and do some moar thorough cleaning. Thanks for the in depth how to KFJ.
 

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Awesome! I remember there was a nice write up on how to clean and troubleshoot the ISC on miata.net or the internet. Might want to try Googling that.
 

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Alright, before I do anything silly, I just want to confirm some things about this problem.

1. As KFJ suggested, I'm going to clean the ISC connector. Is that the one circled here? Also, just spray the **** out of it both (male and female) with electrical connector cleaner?


2. Jaredef, or anyone, where is this " air pipe hose connecting the ISC to the manifold" you speak of? Or I guess the "air supply tube to the ISCV" as read on m.net garage. Which tube is it? Here's a couple pics, if someone could circle it...



Thank you!
 
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