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Old 04-14-2013, 07:38 PM   #1
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Default IAC and Frequency Multipliers

So my 91 with a 2.0BP4W is up and running with a 99 throttle body and IAC connected. However the buzzing on this thing is STUPID loud. I know the 90-97 IAC is at 170Hz and it should be around 500Hz

I know DIY sells a modifier kit
PCBv3 -- PWM IAC Valve Control (TIP120) 'Mod-Kit' DIYAutoTune.com

but I don't believe that will work as a standalone device (aka in parallel with my TEC-2). Currently the factory ECU is controlling the IAC until I get my aftermarket throttle and IAC setup and running on the tec-2

So I'm left with 3 choices:
1)source a 94-97 throttle (which requires IAC plumbing on the intake side)
2)get an external frequency modifier (available where?)
3)live with the noise.

Has anyone setup a freq multiplier? at a cheaper cost than sourcing a early 1.8 throttle?

-Greer

Last edited by g_reichow; 04-14-2013 at 08:14 PM. Reason: list 94-97 throttle limitation
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Old 04-15-2013, 08:31 PM   #2
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So in reading I want to confirm the following:
90-93 IAC ~ 170Hz
94-97 IAC ~ 390Hz
99+ IAC ~ 500Hz

Braineack made reference that the 94-97 is 390ish
ISC and IAC [Archive] - MX-5 Miata Forum

Will swapping my 99 throttle with a 94-97 IAC minimize/reduce/remove the buzzing?

Are the ISC from a 90-93 (have a throttle laying around) compatible with a 94-97 manifold?
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Old 04-15-2013, 08:40 PM   #3
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I ran my 99 idle valve @ multiplication value 11 and it worked alright. If you want proper frequency (~500 Hz) without loss in resolution, check this out: PWM Converter Board

Set value of 1 in TS, and this board to 16 and it will give you 30.5*16 = 488Hz
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Old 04-15-2013, 10:13 PM   #4
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Aaron
Thanks for the post. Without the MS in my solution I will have to provide the +12v, +5v, Gnd, and intercept the signal inline for the in/out on the PCM. I think I can solve that on available wiring in the tec-2 harness. With the factory ecu controlling the signal now (not MS), I have 170hz and a 2 or 4x multiplier with the kit, either 340 or 680 respectively. At this point it is that or make an IAC work. I have a lead on a 94 throttle and have a 91 throttle laying around to test with this weekend.

Thanks,
Greer

Last edited by g_reichow; 04-15-2013 at 10:33 PM.
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Old 04-15-2013, 10:44 PM   #5
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To further muddy the waters, Reverant hits a 97 at 170Hz...so it seems like the 94-97 throttle should work just fine on my application.

If Reverant is right I can buy a throttle and be done
If Braineack is right I have more work to do

-Greer
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Old 04-15-2013, 11:00 PM   #6
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I totally missed the part about not being on MS, my bad
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Old 04-22-2013, 03:24 PM   #7
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It looks like the 99+ IAC accepts a ford IAC style motor as well. I had a ford to GM IAC adapter laying around for a future project. In unbolting the 99+ IAC, the inlets/pattern looked crazy familiar. A quick bolt up showed that it work.

This solves my problem as the TEC-2 runs IAC using GM parts. Using my Ford->GM IAC adapter I can bolt up a GM IAC and have the tec-2 control it. No frequency issues there, just tuning. I'm waiting on the parts to come in, but a happy find.

Those wanting to replace IAC's on the cheap may be able to source the appropriate bit off a ford replacement. Part #'s there requires more research.

-Greer
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