How does the Idle speed control valve operate

koop21 · Postby **koop21** » Mon Jan 28, 2013 6:39 pm

Hi,

I've been trying to figure out what reference(s) or sensor(s) the idle speed control valve uses to know how much air valve should open, but haven't had much luck finding a straight answer. I want to know where is it getting its information from before making an adjustment. I figured out that the A/C is one of the references its basis its calculation on because A/c is linked into the ecu.

But like i said what other reference(s) or sensor(s) does the idle speed control valve read from to make its adjustments?

If i had to guess the ecu basis how much the idle valve should open or close by comparing it to engine rpm? i.e ecu target rpm is 850 so it reads the tacho signal and makes adjustments accordingly?

de Bounce · Postby **de Bounce** » Mon Jan 28, 2013 7:07 pm

First part is to get the correct acronym!
The idle speed control valve is also called the Idle Air Control Actuator/Valve or IAC.

Idle Air Control Systems
The Idle Air Control (IAC) system is used to stabilize idle speed during cold engine and after warm-up operations. Idle speed stabilization is needed due to the effect engine load changes has on emission output, idle quality and vehicle driveability. The IAC system uses an ECM controlled idle air control valve (IACV) that regulates the volume of air bypassed around the closed throttle. The ECM controls the IACV by applying various input signals against an IAC program stored in memory.
IAC System Control Parameters
Depending on system type and application, the IAC system may perform a combination of the following control functions; initial set-up, engine startup, warm-up control, feedback idle control, engine speed estimate control, electric load idle-up, learned idle speed control, and A/T idle-up control.

Further info on how the IAC works can be found on the web

koop21 · Postby **koop21** » Mon Jan 28, 2013 7:13 pm

de Bounce, i believe you are actually mistaken.... Mazda references the idle device under your throttle body as "idle speed control valve", and please read my thread before posting i actually did research this (the whole infact) before posting.

de Bounce · Postby **de Bounce** » Mon Jan 28, 2013 7:17 pm

koop21 wrote:de Bounce, i believe you are actually mistaken.... Mazda references the idle device under your throttle body as "idle speed control valve", and please read my thread before posting i actually did research this (the whole infact) before posting.

Don't care what Mazda call it, to find info about it you need to know what the motor industry call it.
Happy researching!

koop21 · Postby **koop21** » Mon Jan 28, 2013 7:29 pm

nice ninja edit, and thanks for the tip but once again but i have searched those terms also.

I know how the ISC works or in your case the IAC works in general but i'm specifically look for an answer for the mx5, as in what sensor or reference it uses to determine how much it should open.

gslender · Postby **gslender** » Mon Jan 28, 2013 7:45 pm

koop21 wrote:nice ninja edit, and thanks for the tip but once again but i have searched those terms also.

I know how the ISC works or in your case the IAC works in general but i'm specifically look for an answer for the mx5, as in what sensor or reference it uses to determine how much it should open.

The valve is open or closed via a PWM 12v supply controlled by the engine computer. The computer would primarily monitor engine rpm, but also consider other loads (such as AC) and conditions (such as CLT temp) to adjust the signal.

What else are you looking to know?

G

koop21 · Postby **koop21** » Mon Jan 28, 2013 8:12 pm

excellent gslender, in the case of the 1.6 the only factors in engine rpm and a/c? seeing as the idle air valve operates only on cold engines and stops air coming in when the engine is hot?

edit: To add is engine rpm determined by the CAS? or by the ignitor?

gslender · Postby **gslender** » Mon Jan 28, 2013 10:14 pm

koop21 wrote:excellent gslender, in the case of the 1.6 the only factors in engine rpm and a/c? seeing as the idle air valve operates only on cold engines and stops air coming in when the engine is hot?

edit: To add is engine rpm determined by the CAS? or by the ignitor?

No, the engine computer would still account for CLT and Intake Air temp when trying to establish idle. The idle air valve just provide a lot more air needed for cold rich starting.

Other factors are electrical loads, like lights etc. engine computer knows when that's on too. And some 1.6 have pwr steering and there is no feed fwd for that, so computer just monitors rpm and air intake volume (MAF).

All very complex really.

Engine rpm is by CAS.

G