Cleaning And Reattaching The IACV (Idle Air Control Valve)

[wingman358]

Originally Posted by BadDriver123

I saw the IACV wire connector plug wasn't plugged in so i thought i should plug it in. however it randomly started idling at 2500. i tried disconnecting battery,checked the throttle cable and it is slack. No Cruise control cable on my forester. Any ideas? It was idling normally before i plugged in the connector. Vehicle is a 2000 Forester GT with 2006 EJ257 sti engine.

I bet your IACV is stuck fully open

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[LarryRS]

This fixed my issue. I got a CEL for P0507 and P0519. My symptoms were not apparent at first but became an engine idle starting around 1500rpms and often opening up to 2000 rpms in park in 50-60degreeF temps. While driving with the issue existing for a day, I noticed a shudder in the <2500 rpm range while accelerating and some slight rpm shudders on decel between gears.

I got the replacement gasket and did the IACV cleaning. Only I pulled off the IACV a second time when I realized I didn't actuate the valve and verify it was opening without resistance. IACV had plenty of black dirt but no solids to speak of. Got it real clean.
Testing afterwards, the idle seemed to still be high, but after a test drive the high idle and shudder during accel went away.

Thanks OP!

[White-o]

Seems like there are a range of different symptoms leading up to this. I have an 03 wrx with a jdm 205 and it started blipping the throttle from 2-3k rpms on my way home the other day. The rpms mostly stayed in that range, but sometimes would rev up to 4. I got it home and parked it. My mechanic thought it could be a vacuum leak, so I went out with a bottle of brake cleaner and started it up. But this time the rpms didn't blip, they just held steady at 3 until they started climbing higher and the engine was cold so I just shut it off. The next time I started it the rpms stayed at 2k but the engine was running terribly and sounded like it was misfiring, and the ecu threw a P1507 (Idle Air Control Valve Misfunction)

I'm going to order a gasket and clean my valve, but the way the car was running on the last start up has me worried.

Also, I loosened the two soft screws and coolant immediately started leaking out, which I didn't see mentioned in this write up. My mechanic told me it will spill out and you need to bleed the system after replacing the valve.

I'm just concerned that other people seem to just have a consistent high or low idle, whereas my car seems to do something worse every time I start it.

[wingman358]

Originally Posted by White-o

Seems like there are a range of different symptoms leading up to this. I have an 03 wrx with a jdm 205 and it started blipping the throttle from 2-3k rpms on my way home the other day. The rpms mostly stayed in that range, but sometimes would rev up to 4. I got it home and parked it. My mechanic thought it could be a vacuum leak, so I went out with a bottle of brake cleaner and started it up. But this time the rpms didn't blip, they just held steady at 3 until they started climbing higher and the engine was cold so I just shut it off. The next time I started it the rpms stayed at 2k but the engine was running terribly and sounded like it was misfiring, and the ecu threw a P1507 (Idle Air Control Valve Misfunction)

I'm going to order a gasket and clean my valve, but the way the car was running on the last start up has me worried.

Also, I loosened the two soft screws and coolant immediately started leaking out, which I didn't see mentioned in this write up. My mechanic told me it will spill out and you need to bleed the system after replacing the valve.

I'm just concerned that other people seem to just have a consistent high or low idle, whereas my car seems to do something worse every time I start it.

Mine did that. Sometimes it gets stuck wide open which is the cause for the climbing idle. When you pull the IACV off I bet you the valve is stuck open with some crunchy gunk up in there. Blast it with solvent and work it loose. Mines been good for ~15k miles since I cleaned it last, no issues. Let us know how it goes.

[White-o]

Originally Posted by wingman358

Mine did that. Sometimes it gets stuck wide open which is the cause for the climbing idle. When you pull the IACV off I bet you the valve is stuck open with some crunchy gunk up in there. Blast it with solvent and work it loose. Mines been good for ~15k miles since I cleaned it last, no issues. Let us know how it goes.

Thats good to hear lol. I'm about to open the valve up now so we'll see what I find

[White-o]

Originally Posted by wingman358

Mine did that. Sometimes it gets stuck wide open which is the cause for the climbing idle. When you pull the IACV off I bet you the valve is stuck open with some crunchy gunk up in there. Blast it with solvent and work it loose. Mines been good for ~15k miles since I cleaned it last, no issues. Let us know how it goes.

I'm not 100% sure how this valve even works so I can't tell if its stuck open or not. Theres two rectangle openings and within them, in between them, theres a cylinder extending all the way across. I assume thats the piece that opens and closes. But I'm not sure if this is it in its open or closed position lol
If the valve is stuck open, should I be expecting it to snap shut once I clean it enough?

[Charlie-III]

Originally Posted by White-o

I'm not 100% sure how this valve even works so I can't tell if its stuck open or not. Theres two rectangle openings and within them, in between them, theres a cylinder extending all the way across. I assume thats the piece that opens and closes. But I'm not sure if this is it in its open or closed position lol
If the valve is stuck open, should I be expecting it to snap shut once I clean it enough?

No, a small electric motor moves it. You can carefully move it back and forth, bit don't force it.
While a new gasket is great, a thin smear of wheel bearing grease does OK on the mating surfaces.

[ElementGFX]

I picked up my 02 WRX about 4 months ago and its always idled consistentally at 400 since I got it, never any problems like stalling out etc but it does seem pretty low, im gonna try this and see if it brings my idle back up to a more healthy number.

[ElementGFX]

I picked up my 02 WRX about 4 months ago and its always idled consistentally at 400 since I got it, never any problems like stalling out etc but it does seem pretty low, im gonna try this and see if it brings my idle back up to a more healthy number.

[flyjp]

I have a 2005 92x aero and had the fast idle when hot problem, tried cleaning the IACV and still had the same problem so I replaced the iacv. Now it runs fine for the few minutes then dies. Try to restart it just dies again. The idle hunts at like 100-300 and dies. When I put the old iacv back on it run perfectly until I get in stop n go traffic in 75 - 80 temps and then it creeps back up to 2000-2500 rpm at idle. Any thoughts? Do I have to re flash he Ecu, I'm running Cobb stage 2. I tried an idle reset also but it didn't help. Thanks for any help.

[Taylorsi]

Originally Posted by flyjp

I have a 2005 92x aero and had the fast idle when hot problem, tried cleaning the IACV and still had the same problem so I replaced the iacv. Now it runs fine for the few minutes then dies. Try to restart it just dies again. The idle hunts at like 100-300 and dies. When I put the old iacv back on it run perfectly until I get in stop n go traffic in 75 - 80 temps and then it creeps back up to 2000-2500 rpm at idle. Any thoughts? Do I have to re flash he Ecu, I’m running Cobb stage 2. I tried an idle reset also but it didn't help. Thanks for any help.

It is you cruise control cable, very common on GD, or GG, chassis cars in high ambient temp stop-and-go traffic. Loosen the cable at the throttle end until the issue goes away. Also, get a turbo heat shield if you don't already have one. Cruise control module is right behind the down pipe and turbo.

[wingman358]

Originally Posted by Taylorsi

It is you cruise control cable, very common on GD, or GG, chassis cars in high ambient temp stop-and-go traffic. Loosen the cable at the throttle end until the issue goes away. Also, get a turbo heat shield if you don't already have one. Cruise control module is right behind the down pipe and turbo.

Has this diagnosis and "repair" ever been proven to work? I had the problem and tried that fix because everybody says that works. Didn't work. I even *completely removed* the cruise control cable and module and still had the issue. So pretty clearly not the cause, at least in my case. But this is the wrong thread for that.

[IsThisNic]

03 wrx is throwing the code p0508, IACV is replaced, new gasket, still getting an idle jump. Moving on to the electrical side of things. But if anyone has any advice it's greatly appreciated.

[basedx]

02 WRX here that really likes to idle at 1150 despite my best wishes to have it back down at 700-750. The strange thing is that with AC/heat on the car will try and idle at 850, but bump back up and down again to 1000-1100. I will try and clean or replace the IACV first following this guide.

[cclemons]

Thanks for the write up! I have a 1507 code on my 02 that I just picked up, so I'll definitely be giving this a shot!

[coolfeet]

Originally Posted by wrx5150

To late, dealer charger me amost $500 to replace it.

My 1999 Legacy 2.2 started and idled rough as soon as it got below freezing. It through the P0505 CEL code. Been there, done that on 2 Ford vans.

I cleaned the IAC valve on my 1999 Legacy 2.2 with a MAF sensor cleaner and a shot of brake cleaner. I used a Scotchbrite pad to clean carbon off the sealing side of valve body.


I did not remove or take the gasket off as I did not have a replacement gasket.


The 26 year old vacuum line broke while removing. It felt like it was made of plastic. Maybe it is. I replaced it with 2 new spliced vacuum pieces I had from a left over project.


The 2 screws were tight taking off. I made note of the replacement hex screws and will replace them while replacing the gasket.



The vehicle fired up after a few turns and runs great. I will take it on a long test drive after the snow melts on my driveway.

[Amac13]

WRX MY99 new battery, idles well at first then will will not idle.

I've been runing it for days with Aircon on to reset systems but to no avail. I cleaned the idle air speed control valve which was very dirty but still not good. please help

Adam from Australia