Setting idle air quantity with IAC or Throttle

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Setting idle air quantity with IAC or Throttle

Postby fasterlaster » Sun Nov 19, 2017 7:53 pm

I have a general question as I'm am slowly getting this engine tuned, I'd appreciate some input in. Engine is a 2017cc aircooled VW engine, with a stock single throttle body from a FI beetle, and Stepper IAC. The throttle body setting per stock sets it nearly completely closed, with no aux air path past the butterfly. As it sits now the IAC must be fairly open to allow the engine to suck enough air to idle while the throttle is closed, with no alternative path.

Am I best to proceed with my initial tune which requires the IAC to be open to run, or to open the throttle a small amount so that IAC is only active at colder startup or for any load adjustment?
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Re: Setting idle air quantity with IAC or Throttle

Postby MegaMicra » Sun Nov 19, 2017 8:14 pm

Although mines not a VW my stock Nissan setup has a single throttle body with the butterfly completely shut. My idle comes solely from the iacv. It worked well for Nissan and works perfectly for my MS3X install.
It's probably just up to you which path you take.
In the event of electrical failure to the iacv mine defaults to partially open so the engine doesn't cut out.

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Re: Setting idle air quantity with IAC or Throttle

Postby elutionsdesign » Mon Nov 20, 2017 6:55 am

Typically I set the throttle plate to a low idle, lower than I'd like but in the event of total IAC failure it will still idle, then let the idle valve take it from there.
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Re: Setting idle air quantity with IAC or Throttle

Postby fasterlaster » Mon Nov 20, 2017 4:21 pm

Thanks a bunch for the input on this. Sounds like it's dealers choice. I'll just have to give both a shot and see if one is inherently easier.
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Re: Setting idle air quantity with IAC or Throttle

Postby kaeman » Sun Nov 26, 2017 8:11 pm

I am with Elutionsdesign...

I set my butterfly's to an idle speed below my target idle and then use the iac to bring it to the correct idle speed for engine load and warmup. That has worked well.
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