Can Idle Air Control Valve be adjusted?

[steamin53]

96 Legacy outback 2.5 auto.

 

History: Had a high idle condition. Cleaned IACV with no improvement; removed and tested IACV and it passed resistance tests but it was "reluctant" (didn't move consistently with stimulus signals applied to the pins).

 

Replaced valve with used but clearly correctly functioning valve. Improved idle but still not right.

 

Wiring tested ECM to IACV and proven good. ECM output voltage tests indicated defective ECM. ECM replaced with used one and tremendous improvement with idle at or near spec.

 

BUT, it will occasionaly set code P0515 Idle Air Control.

 

Now once the vehicle is fully warmed and has been driven for ~10 (or sometimes much more) miles when coming to a stop from highway speed the idle drops to 500 RPM and the computer sets code P0515.

 

The vehicle runs great and idle is smooth as silk. I wonder if I need to somehow adjust the IACV I put in. I note that the metal plate on the top of the new one isn't in the exact same position as the original.

 

The manual says it should be adjusted for 45% duty cycle. (greek to me folks). So my question arises as this: If I adjust the plate to the same position as the original will it make a difference and perhaps solve this problem?

 

Steve

[screwbaru2]

You could try marking where it is now and then put it where it was before it was changed. I think there's something more going though.

[edrach]

My problems with the IAC are usually high idle conditions with no CEL codes. Seafoam in the next tank of gas eliminates the problem every time after the gas is run through the engine. After about 6 months the problem comes back and I add the Seafoam again.

 

I would think the Seafoam would free up the IAC; after that, you can still try adjusting it if needed.

[steamin53]

I love seafoam too and use it for many different applications.

 

However, I suspect that the valve is not hanging up. Everything seems to be working fine except that when the engine is fully warmed up the idle is just a tiny bit low. Remember this is a clean and smoothly operating valve installed a couple of weeks ago.

[porcupine73]

There is the whole 'can' and 'should' thing. There is no adjustment that 'should' be made. The ECU has a control loop acting on the IACV based on idle rpm.....so unless it shuts the valve or opens the valve as far as it is willing to go and still can't control the rpm at the setpoint then the iacv 'adjustment' should be the issue. Thoguht they sometimes get gummy and sticky and don't open or close properly of course. Not sure how seafoam in the fuel tnak would help with that though since the fuel does not pass through the iacv. There is a recommended procedure for cleaning it on endwrench (at least for the speed dnesity based setups but the same basic idea applies to them all except drive by wire of course).

[steamin53]

Well boys, here's the outcome. At the recommendation of the fine folks at CCR, I discussed this with the tech specializing in emissions service at Strictly Automotive; a Subaru specialty shop in Denver. We both agreed that since Subaru requires that the duty cycle be set after installing a new IAC that adjustment must do something but we also agreed that the computer will compensate for any adjustment made to bring the idle (if possible) to the desired rpm.

 

So that said, I felt that the only thing adjustment might do is to change the manner in which the IAC valve responds rather than the ultimate outcome of the response in terms of idle speed.

 

So, taking the upper plate position of the old IAC valve as a target setting I scribed the original position and adjusted the new (used) IAC valve to that setting. Tadahhhhhhhhhhh... no service engine light, but I didn't like the rate of response to loading (ac on/off etc.) so I tweaked it somewhat in both directions of travel testing again each time. It is very sensitive to change... a little movement goes a long way. Still no fault light. Test drove it with multiple shut downs and repeated highway to stop sign stop and go situations with no fault light.

 

I don't know for certain, but I think it may be solved.

 

If it isn't, my next step is to find someone who can read the duty cycle with a scanner and set it to the factory spec. If that fails we'll look at the throttle position sensor.

 

I'll let ya know if it fails again.

 

Thanks to all for input.

 

Steve

[lmdew]

Well after some time is it still working OK?

 

Thanks

[Lare]

On the top of the 2001 EJ25 M/T just past the throttle body plate where the wire harness connects to a plastic magnetic part that slides over the spindle from the main valve. That part of the module has slotted holes for a reason. If someone knows that reason please let me know.

Edited April 23 by Lare