How does the IACV-ACC decide on an optimal idle?

[aacaac]

In theory, ecu ignores o2 sensor readings so how does it decide on a good idle. My ACC is definitely working but it insists on being 50 percent open during idle which shoots my idle to 1000 rpm. If I unplug the acc, the idle is around 700 but the ecu cries for air by sending a message to acc to open up 80 percent. The ACC goes down to about 30 percent when I go into open loop. It stays at 50 percent open even when I go into timing mode. I have 4 computers and they all do this. I'm thinking I'm rich during idle but curious how the ecu determines this.

[Def]

Are these all stock ECUs? Basically the AAC valve duty cycle is determined by the ECU trying to hit the target idle RPM for that coolant temp.

If the ECU continually wants an idle around 1000 RPM, I'd check the coolant temp sensor that goes to the ECU. Otherwise try closing the AAC bypass screw down some(clockwise) and see what happens to the duty cycle.

[aacaac]

Are these all stock ECUs? Basically the AAC valve duty cycle is determined by the ECU trying to hit the target idle RPM for that coolant temp.

If the ECU continually wants an idle around 1000 RPM, I'd check the coolant temp sensor that goes to the ECU. Otherwise try closing the AAC bypass screw down some(clockwise) and see what happens to the duty cycle.


yeah, they are all stock. My temp is around 183 F. I know someone running at 154 F and their duty cycle is 61 percent.

I assume the bypass screw is the idle adjustment screw. i will give that a try. If that makes a difference, then that would mean my 50 % duty cycle is either fixed or set to something like average temperature after warmup. even when i turn off a cylinder, it stays at 50 percent. The fsm says duty cycle should be 15 to 40 percent. i'll have to review what open loop means

[aacaac]

Ok, I adjusted the idle adjustment screw and dropped my idle from 1100 to 800. The aac stayed at 50 percent so my idle is stable at 800. When I decellerate to a stop my idle falls to a lower level now. ie 300 instead of 600 and then goes back to 800. I logged the aac values and they fall to 30 percent when my idle is at it's lowest point so essentially my aac stays open less as I decellerate. Not sure how one fixes this.

[aacaac]

One thing I noticed from reading fsm's is that the s13 does not keep track of electrical load while the s14 does. Might explain why my acc does not respond to me turning on my lights.

[Def]

It sounds like something is up with some sensor that is keeping the AAC from properly tracking the target idle speed.

The duty cycle is slow to respond when dropping revs, but changing the idle screw doesn't change my idle RPM(within reason). No idea what my duty cycles are, but I know when putting in cams I had to open up my idle adjustment screw to keep the engine from dropping down in revs as I clutched in.