Hunting an IACV issue

[Dalee1104]

Hey all! I've been a long time member in the 2nd and 4th gen forums but haven't posted much in this one.

Backstory on me, I've worked in a subaru repair shop for a few years before leaving and have some ase certs so I can definitely throw some wrenches but this one has me confused.

 

The car in question is a customer's car, a 2003 outback (I know not a legacy but these forums truly are the most helpful). The car has been sitting for multiple years before they towed it here. It has about 190k miles and came in having issues with a p1507 code, idle air control valve failsafe fault. The customer is trying to save as much money as possible so I started with cleaning the throttle body and making sure there is no gunk in the IACV as well. Pulled the IACV and cleaned it and when cleaning I found the piston has actually cracked and basically fell apart. We tried a valve from O'Reilly and matters were worse at no surprise to me. 

I found the plug wasn't contacting the pins completely and got a code for the voltage being incorrect so cut out the old plug and wired in a new one that actually does snap in place. Returned the O'Reilly valve and got 3 more from a local junkyard still trying to save money. Oem is a 330$ valve and junkyard is 15$ and free for the ones you sneak out lol.

I hooked the engine up to my smoke machine and smoke checked for any vacuum leaks, all seems to be nice and tight with no visible leaks. Fuel trims seem to confirm as well as they don't look too far off from what they should be. 

The car idles beautifully with the oem junkyard IACV but when reved up to about 3k rpms, the car will stumble and start sputtering before it eventually recovers. If you smack the throttle and damn near floor it, it will rev past that point just fine. 

 

With that I wanted to pick some of the other members brains here. The code is specifically just the p1507, idles okay, revs hard okay, but typical driving is not okay. I was thinking maybe fuel pressure if the fuel pump was dying or the gas is 3 years old so maybe the gas. But again why would it only trigger just that code in that case? Do yall really think all 4 IACV were bad? That would be some really bad luck which has me thinking something else is going on outside of the idle air control valve. Any and all help is greatly appreciated! 

[Dalee1104]

Oh also I might add the previous mechanic replaced the throttle position sensor before he gave up and they towed it here. No codes for it but figured it was worth including 

[doublechaz]

I don't see how this would work, but I found a guy who says that a bad neutral safety switch can give your symptoms.

So if it is a manual, it should only take a couple minutes to test that NSS to see if it is switching or not.

 

From my personal experience I would be suspicious of the timing belt depending on the conditions while it sat for so long.  If the belt is jumped it can make the car run like you describe although in that case the IACV code would be not connected to this, and you would probably be getting infrequent random misfire codes.

[silverton]

three year old gas is not good.

I also found that guy, but it's manual trans specific https://www.subaruoutback.org/threads/diagnostic-code-p1507.30777/post-341124

[Dalee1104]

Apologies for not including all the info. I have seen the 5speeds with the NSS but this one is indeed an auto.

I agree on the timing part, I feel at that point I would be seeing some random misfires or really any sort of other indicator but it truly is smooth as hell until it hits that 3k rpm point. It will kind of peg bag and forth if you hold the gas steady. It's 3k, dips down to 2k, revs back up to 3k, and so on until revved hard, or let stumble down to idle to figure it out. 

I was wondering if old bad gas could be an issue with it as well. I know it's definitely not great. This whole p1507 code I feel is just the result of something else going on. A tad confusing this one 

[doublechaz]

Alcohol in gas pulls in water from the air.  I'm not sure if the alcohol also promotes varnishing or some other chemical process.  But I've had modern non stabil treated gas that wouldn't run a lawnmower after sitting for 4 months.  Fresh gas fired it on the first pull after a full drain and fill through the system.  I live in the high desert so mowing only has to happen a couple times a year.  Now I get fresh for each job, run the mower dry, and dump the can into one of the cars.

I am surprised that three year old gas will fire your car at all.  I wouldn't just add fresh gas, I would drain as much as possible.  If you have a big enough container you can pull the hose out from the filter and replace it with one into your storage.  Key on should pump it out as it will fail to build pressure.  If the car gives up after a timeout you may have to sit and cycle the key until it's done.  Once it starts to spit kill it so you aren't running the pump dry.  Back together with a couple gallons of fresh gas and see what happens.

[Dalee1104]

Okay I'll give that a shot thanks for insight Chaz. We are in pnw a couple hours of Seattle so not much elevation. The gas fires surprisingly well here even after sitting a few years but it's less than ideal.

 

I'll try to get all that gas out and get some fresh gas in and update 

[xrayspecs]

I had a gummed up IACV in the past, i replaced it and had some stuttering issues. The PCV valve was sticking open as it was also gummed up which lead to the grimmy IACV i had. Cleaned it out and my problem went away. YMMV but a quick check will tell you if thats the problem. 

[Dalee1104]

Figured I'd give an update or maybe the lack thereof even. I ended up getting fresh gas in it, ran a bottle of HEET through it, and pulled the pcv valve to clean it and make sure it was working okay. Everything was plugging away and checked out but the car still had this weird hesitation when trying to accelerate. My next move was going to be to swap out the throttle body. I've seen this issue at our shop and a quick throttle body swap did the trick, quite curious as there must be a crack in the throttle plate or some clogged ports somewhere despite my efforts on cleaning.

This car has been sitting for over 3 years and the customer hadn't even driven it because it wouldn't run. Well we drove it around the block the other day to see if it was really drivable and while it is I discovered the transmission is in pretty bad shape. Binding hard on sharp turns, extremely hard shifts, and just not smooth. 

With that bit of information the customer decided he didn't want to spend any more money trying to hunt an issue when the car may not even be worth it. It was in really rough shape as it was, he just wanted to see if he could get it going without dumping money into it.

And with that the hunt is over on my end, customer is going to drive it as is until it dies and then buy a new car. I appreciate the insight and help searching for this problem yall. 

[doublechaz]

It is more damaging to a car to park it for a year than it is to drive it like it is stolen for a year.

[Dalee1104]

I agree with you completely, and this one was parked for like 4 years lol