Using the bosch IAC valve (piazza) for EFI cold starts...

Engine related articles specific to induction (carby, EFI etc.)
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Was dangerous_dave
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Joined: Mon May 30, 2005 12:38 am
Location: MEL

Using the bosch IAC valve (piazza) for EFI cold starts...

Post by FieldEffect »

The purpose of an Idle Air Compensation system is to allow more air past the throttle body whe the engine is cold. The gemini in standard form has one in the air filter.

Useing one helps avoid the problem i have at the moment where if i adjust the bypass screw in the XF tb so that it starts nicely cold, it idles at 2500rpm warm. And if i adjust the screw to idle nice at 800rpm warm, its a bitch to start.

So for a while i had abit of a compromise happening, it was partially a bitch to start, the idled at 1500rpm warm :)

I thought my piazza IAC was seized as it drew current when i powered it up but didt move. But i did some reading and actually found out how to use it properly.

"Some people have been using an auxiliary air regulator for fast idle control. SAAB, VW, and many other European vehicles used this system on their early EFI systems (D-jetronic) and on their mechanical injection system (CIS).

The great thing about this system is that it does not need to connect to MegaSquirt at all. You just hook up 12 volt, ignition switched, and you are ready to run. Use 12 volts from the fuel pump relay. If the engine is not actually running you do not want it powered up, as it will move to the 'warm' position even though the engine isn't running."


Just thought i would post for anyone who has one and didnt know what they are for or how to use them, like me 30 minutes ago :)

You could even go one step further and reduce the average voltage applied to it if you wated it to open slower if your egine is slow to heat up.
Gemini: Light weight, low cost RWD automotive platform.
Gemi Coupe
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Post by Gemi Coupe »

Crumz wrote: I like your theory, just remember though, you will need somewhere to draw air from and then somewhere to plug it back into the flow, both of which need to be after the air filter.
Depending on what setup of TB, Intake manifold, intake tract and air filter you are using, this could be either easy or hard.

if you are using a standard rodeo manifold and plenum there is a hose on the underside of the plenum, between the runners (No2 and No3) that you can connect to, the other pipe will connect to anywhere between the air filter and the throttle body (for anyone using a different throttle body)
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