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Old 02-09-2012, 07:56 PM   #1
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Default 1500 idle then drops to 1100 then 950 need help

So like the title says. my miata today started staying at 1500 rpms for about 5-6 secs before drop to 1100 then at the set 950 rpms. when i rev past 1500 it wants to stay there even when the engine is hot. btw its a 2001
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Old 02-09-2012, 08:38 PM   #2
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I have no idea what type of stuff is done to your car, but off the top of my head, I'd say your IAC is sticking or your throttle cable?
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Old 02-09-2012, 08:39 PM   #3
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Despite utter lack of information, here we go..

Do you usually drive in stop and go traffic?
Is the car used primarily for short trips?
Do you just change the plugs and the air filter when it's time for a tune up?
How often do you change the oil?

Aside from the one of the obvious culprits, which is a post TB vacuum leak, you may want to check the TB itself for gunk.
Next, IAC pintle may be clogged.
Also, gasoline contaminated oil will mess with idle, as well.
There is also a chance of the CTS - or its connection - going south. Checking AFR whn the idle stays high will give you an idea.

In short,
* check for a vacuum leak,
* check the PCV and its plumbing,
* clean the TB and the IAC pintle,
* make sure your oil is not contaminated,
* check the CTS and wiggle the connector,
* check engine grounds around the TB, if you had any sort of work done on the engine lately,
* Oh, and check the throttle cable to make sure it's not sticking.

I just hate blasting a shotgun at a problem instead of pointing a laser to the specific cause, but, like I said, there is just no info to work with.

Good luck..
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Old 02-09-2012, 08:44 PM   #4
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OK. sorry for the lack of info. the car is a flyin miata voodoo 2 kit. the boost gauge shows good vacum and it happen's and time the car goes under 1600 rpms it will hang at 1500 for a bit. i just disconnected the battery and the problem for the moment has went away. and it started randomly. so im thinking its a sensor. other things i have done to the car is a 255lhp walbro , 305 supra injectors, voodoo box , and retard timing wheel. mishimoto rad.
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Old 02-09-2012, 08:58 PM   #5
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You can remove the iac easy enough and give in a good cleaning with brake clean or carb clean. If you plug it back in while still removed and have the key on, the pintle should move a bit, if it doesn't then either try cleaning it again or replace it.

Do you still have a/c?
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Old 02-09-2012, 09:23 PM   #6
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Definitely sounds like when my IAC broke. Very annoying.
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Old 02-10-2012, 01:32 AM   #7
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I do have a/c and the upper intake manifold along with iac were both cleaned very good when i installed the injectors a few months ago. like i said i have driven about 45 mins and the problems has not come back since unplugging the battery. Not sure why it happend in the first place but i dont think its mechanical
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Old 02-21-2015, 12:21 PM   #8
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Holy cow this is exactly the same issue I've been dealing with - did you ever figure out the cause?
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