3 Wire JECS Idle Air

[Glenno]

I have a MY98 STi WRX Engine (EJ20) with a JECS 3 wire idle air control on it that I want to utilise.

The setup is not in a WRX so I am using an SMC and not a Plug and Play to run the engine. I am using the PWM output to run the boost control, to get a stable idle control I want to try and utilise some of the spare outputs to compensate for Aircon and headlight load.

What voltages and connections does the valve use and what strategies are normally used to control it?

[Ian]

I have previously used a selection of 5w resistors to bias the valve open for air-con with a condensor fan. The valve is somewhat non-linear in operation when operated as one-sided only. It sort of opens slowly and then really opens. I may have had to fit a fixed resistor on the other side to stabilise it but it was a fair time ago and I don't recall exactly.

It has two shutters inside so if you are still running coolant through it you will get an idle up effect when cold.

[Glenno]

Thanks for the help, it appears the one way valve is missing from both of the V4 manifolds I have (I know why it would have been removed) but I can't remember what they look like and I definatley don't know the part number to get another one or the part number for the square section O ring that goes there with it.

[Wroom]

I know you got an SMC, but it can be useful to know that when running the MY98 JECS IAC with two outputs from a SM4 one has to use at least 150 Hz to make it stable. If you can swap it out for something better, then do so. I think a Bosch two wire IAC and an bunch of resistors would be easier to get working good.