IAC frequency - Miata Turbo Forum - Boost cars, acquire cats.

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Old 08-02-2009, 03:56 PM   #1
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Default IAC frequency

Figured I better start a new thread rather than keep jacking the other one. I just finished trying several IAC frequencies and thought I would post the results.

100 Hz - LOUD.
200 Hz - Quieter, but still noisy. It set up this weird resonance in my CAI system (cold air intake ducted into the turbo from the cowl) that made me think it was something really wrong with my new turbo at first. Strange thing about it was even though it was the IAC I could not hear any noise at the throttle body. But the duct to the turbo inlet was humming loudly through the air filter and vibrating noticeably to the touch. Then I changed the frequency to...
250 Hz - Basically inaudible. Weird turbo inlet ducting noise gone.
1000 Hz - What I had it at for awhile before. Not sure why (or do not remember why) it was ever set to this but it worked.

Changing nothing else, the idle speed drops as the frequency is raised; it idles faster at 100 Hz than at 1000 Hz.

That is it, quick and simple post.
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Old 08-02-2009, 04:56 PM   #2
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MSPNP uses 385Hz... for a reason probably?
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Old 08-02-2009, 05:35 PM   #3
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I believe he is talking about the NB IAC.
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Old 08-02-2009, 05:36 PM   #4
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srry /me=fail
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Old 08-02-2009, 06:27 PM   #5
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Yes NB IAC
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Old 08-02-2009, 07:53 PM   #6
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Quote:
Originally Posted by ZX-Tex View Post
Changing nothing else, the idle speed drops as the frequency is raised; it idles faster at 100 Hz than at 1000 Hz.
Any difference noted in idle response or stability at the various settings? Mine's set to 500hz mainly because of the below post but seems to work as well at 1000hz. Starts honking at 250hz and below.

What is the stock PWM frequency of a '99+ idle motor? - MX-5 Miata Forum
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Old 08-02-2009, 08:01 PM   #7
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I was wondering the same thing. I'll be daily driving the car again starting next week so I can play around with it a bit and see. I would think though that to really do a proper comparison one would need to retune the idle PID parameters for each frequency. Not sure if I want to go that far or not

Other than the noise, and what Travis mentioned in the other thread about the controller loop not running above 200 Hz anyway, are there any significant tradeoffs here?
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Old 08-02-2009, 09:19 PM   #8
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Mine is set to 500hz
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Old 08-02-2009, 11:20 PM   #9
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Mine is 1000. It doesn't hum/moan/buzz at 500 put other threads pointed to 1000 so I left it there.
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Old 08-02-2009, 11:28 PM   #10
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18psi, Yep the Mazda cpu uses 400Hz approximately (I measured it with the oscilloscope I have) and I know about the noise. Good to see your on the road and learning, you will end up with a good working knowledge of the engine sensors and the e420c . What are you going to attempt to adjust now and how did you go with the fan set up? Donít forget to save those files before you change things.
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Old 08-02-2009, 11:43 PM   #11
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Quote:
Originally Posted by Tedsmx5 View Post
18psi, Yep the Mazda cpu uses 400Hz approximately (I measured it with the oscilloscope I have) and I know about the noise. Good to see your on the road and learning, you will end up with a good working knowledge of the engine sensors and the e420c . What are you going to attempt to adjust now and how did you go with the fan set up? Donít forget to save those files before you change things.
Ted
Thanx man. Looking at how you did yours and the way Travis adjusted mine, I have them coming on at the same time at around 90* or so. I cleaned up the "aux out" settings so that they don't come on in boost, and I dont have 3 "or's" in there. Much cleaner now and works great. Temps are steady at 100-105, and never go past 108*.
I have autotuned the majority of the cruise cells and have the idle steady


Back on topic though:

What do you guys have your "post crank enrichments" set to?
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