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Idle control issues


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Hi guys (newbee here)

I have a issue and wondered if its a simple case of a new icv or if I'm missing something and was hoping someone could help??

when setting up the idle, I make sure all other supports are turned off, I put it in open loop idle control and open idle control base position table. I start the car and adjust the numbers until it idles exactly where I want it throughout the temperature ranges. get it up to running temperature and its perfect. I rev it, drive it and it comes back to a perfect idle at -75kpa. I then turn it off and back on and the car revs at 2k at -65. I go back into the idle base position table and turn the numbers up until she idles at 900 rpm again and its perfect. park it up and when it gets hot its doesn't wanna idle at all. I turn the numbers back down and she's fine. going round in circles, am I missing something? 

sorry I haven't got my laptop with me right now or I would upload log files. the problem is. the car idles fine at either setting once set up so I don't think its the idle control valve. but why am I seeing different manifold pressures at different times? things I was going to check next is a vacuum leak, re check all my vacuum lines, check the throttle is shutting properly,  but I just wondered if anyone else has had a issue like this and what they did to fix it?

I'm using a link v5/6 plug in ecu.

thanks in advance guys


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The V5/6 cars have a stepper motor idle valve.  With a stepper motor there is no position feedback - the ecu can only guess its position by keeping count of how many "steps" it has sent to the motor.  The trouble is the ECU can only assume that the motor moves the right amount everytime it sends it a step - if the valve hits say a mechanical stop at one eng of its travel or there is a sticky region within its travel range the ECU's count may no longer match its actual position.  So to me this sounds like what is happening to you.  So its possibly sticky or it is being commanded to move beyond its actual mechanical range.  I dont know how serviceable they are on a subaru as I have never seen one but if you can make sure it is clean and it can move smoothly through its full range that would be a good start.  Then we want to make sure that the numbers in your base table look like they are within its realistic step range.

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Wow Billy. I have been chasing the exact same issue on and off and doing exactly the same thing chasing the idle up to 90*c.

I now have a clamp on every possible boost leak point and have a clean valve. This has been frustrating the hell out of me although it is fine at the moment.

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I took it out and cleaned it, turned on the ignition and it moved out and back when i turned it off. but still wouldnt work. I grabbed a second hand part from my local subaru specialist. when i took the old one out it sat about 5mm further back than the new (second hand one). i checked the part numbers where the same which they where. i plugged it in and it travelled alot further out, turned it off and it went all the way back and returned to the same position it was before. i fitted it and set up the base idle position table again and touch wood shes started 6 times now and achieves the rpm ranges set. it was frustrating because the part seemed to move and work as it should but.... i no longer have to set the base table with different numbers everytime i start ;-) 

happy days 

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  • 4 months later...
9 hours ago, Simon Kribstock said:

Having this same problem. This is frustrating as my engine idled just fine with a standard ECU.

Is buying a new IACV the only solution that has worked for everyone?


I would say it is unlikely a failed valve, I would rule out other possibilities first.  Please keep your replies to your other thread to avoid confusion:  


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