IAC control?

[Modfox Dude]

Hi. How is the IAC on a 93 Mk Viii controlled? Is it just 12V-switched open and closed otherwise? Or is it PWM? Or...???
Thanks.

 

[joegr]

PWM

 

[kTaLgsTo]

It's sent directly from the PCM, there's nothin inbetween

 

[Modfox Dude]

Gotcha. I'm asking because I'm running an older standalone ECU with this engine in a fox body. I want to interface it to the ECU, which has a single on/off signal. I suspect that even with PWM I can run straight 12v/Gnd to it and open it fully, but not sure if that will be too much air. I can build a circuit to generate PWM, but let me run some tests first. Thanks.

 

[joegr]

You'll need to PWM it to actually control idle speed.

 

[joegr]

It's sent directly from the PCM, there's nothin inbetween

And the PCM (Powertrain Control Module) is using PWM (Pulse Width Modulation) to control it.

 

[Modfox Dude]

My standalone ECU only does on/off for IAC. I'm considering building a simple PWM circuit (I would set PWM duty-cycle with trim pot) and ECU would just activate on/off. But I was able to test it full on (with continuous +12V) and I get a few hundred RPM increase, which is pretty decent.

 

[joegr]

I wonder if the IAC would overheat if left at full current for too long? Possibly not a problem, but it probably wasn't designed for 100% duty cycle either...

 

[Modfox Dude]

Good point.
There's one way to find out for sure

 

[Modfox Dude]

I really just need to play with the throttle for 10-ish seconds, so that shouldn't be too bad I guess. But I'm not sure yet how the ECU will handle it.