ISC Valve Base Frequency?
 

Quick question, can't seem to find my answer anywhere.

What is the base (constant) Frequency of the ISCV for a FD?

I found in this thread:
https://www.rx7club.com/showthread.p...=bouncing+idle
at post #4 there seems to be an excert from a repair manual or a features manual of some sort that outlines the base frequency to be 244hz.

I did look at the 1993 and 1994 Repair manuals and it didn't have the same information for what the frequency is. So I guess that may have been for a FC?

If someone could confirm what the frequency is that would be great, TIA.

https://www.rx7club.com/attachment.p...1&d=1247974931

that is in the 93 service highlights document found in the tech manual sticky, page F-45

more people need to read this document, it explains a LOT about the car

argx I am going to buy an FD from you and over pay....that way I wont feel bad when I wear you out with questions when I need to fix it :-)

Are you a genius or something :-)

Glad there is people like you here to answer questions.

Excellent, Thank you very much arghx. I missed seeing the service highlights document.:)



Another question for anyone willing to answer:
Is the ISCV on the 93 the same through all years? I don't have a parts catalog for a North American FD.

Is the part number N3A1-20-660 applicable to the 1993 North American FD.

In reality the real question is: Is part number N3A1-20-660 a 244hz base frequency solenoid valve?



***a little info***
I'd measure the base frequency on the car, but it is not being controlled by the OEM ECU.

Someone set the base frequency to 170hz and I thought it didn't sound right (the actual buzzing noise)

I need to be sure it really is 244hz. (not for tunning, but for arguement sake)


Thanks guys!

I figured since I'm up at 4am to just call to a Mazda dealer in the states.

They confirmed the part number to be the same.

So all questions answered. Thank you again arghx

Thank you for the compliment. However, it doesn't take a genius to read service manuals, technical documents, and other sets of instructions. I have collected a library of them on my computer in PDF form.

It's not the solenoid valve that determines the frequency, it's the PCME (ECU). The 244 Hz waveform is sent to whatever valve is there to receive it. The solenoid is just a coil with a rod through it, no more. It is not "base frequency" specific; it responds to the average current through the coil: higher duty cycle = higher average current.

Section 1380-5 of the 1994 RX-7 parts catalog shows P/N N3A1-20-660 for the IAC valve; Mazda changed terminology from "ISC" (Idle Speed Control) to "IAC" (Idle Air Control) on the Miata and the RX-7 in 1994.

^ accurately inaccurate.

You need to know the base frequency for running a solenoid valve. If the frequency sent is to high you will burn up the solenoid. etc...

The idle speed base frequency can be set on some engine management systems. In my case that is what I'm dealing with.

I have going on (cleaning up someone elses mess):
1. a bouncing idle (leading me to check things over.)
2. The solenoid valve does not have a pleasant buzz to it (leading me to check the frequency)

Thank you for the terminology lesson.

If the solenoid valve was designed to run at 244 Hz, run it at 244 Hz.

Yes, I changed it today.

On a side note:
This paticlar FD will start to have the idle bounce between 1400-380rpm once the IAC reaches 90% opening (worse above 90% and can't idle at over 95%). So I limited it to a maximum opening of 88% and that cleared that up.

I also found the Idle speed set screw tightned all the way tight. I backed it out quite a bit actually to give the IAC more room to move up/down.

I then increased the virtual dashpot compensation higher.

Now there is no more bouncing idle and the car is easier to drive normally because the engine doesn't want to die out.

Opening an old thread.. but this could explain the bussing sound I got when i Switched to Halteh last year... Since the BAC frequency is set to 140hz apparently ... not 244hz...

because I cleaned it up and still weird noise... so will change that setting and see what happens... couldn't get worse right? :D

are you getting the sound with the key on, engine off?

No, acually when engine is running, and as soon as the ISC is active it sounds weird...
But the engine is out now for overhual, since bad compression after rebuild. So ISC had to be up at 75% with warm engine to keep idle.

Perhaps that high duty also can sound a bit
But still 140hz is set in the haltech ps1000... And it should be 244hz, right? :-)

the Mazda valve is pretty intolerant of the wrong HZ setting, the worst it does is sound like a "marital aid" oh and not control the idle speed...

Hmm what is martial aid??

It is controlling the idel, but buzzes when it is activated... But wheb warmed up it sounds less

Will get my engine back in 2 weeks, then I'll se what happens when changing to 244hz abd perhaps also getting the duty cycle diwn if my compression issue is fixed

the valve always makes noise, but its quietest at the proper HZ. you can get noises all the way from jackhammer to blender out of it

Back from the dead! (Thanks to a search)

I'm getting a really funny electronic keyboard-like noise from somewhere around the upper intake manifold (UIM)/Manifold extension. It only "plays" when the engine is running, and sounds kind of like two "notes" being played on an electronic keyboard/synthesizer. They seem kind of random, and I can't distinguish a pattern in the difference between the "beat" of the two notes.
This is a video of the noise:
https://www.instagram.com/s/aGlnaGxp...530_8282023579

Could this have something to do with the the above?
If so, where is the HZ setting of my Adaptronic modular PNP ECU for the IAC/ISC valve? This is a '99 13bREW on stock (almost) everything except the ECU.

Thanks!!

First off, easy way to see if it's the ISC is to unplug it and see if the noise goes away.

Dale