I drive a 2003 Subaru Impreza Outback Sport and my husband drives a 2005 Subaru Legacy Wagon. Recently my husband has set his eyes on a VW GTI. Thinking he just wants a smaller sporty manual transmission I thought perhaps he should drive my car for a bit. (I know it isn’t the same but it’s paid for!) He’s borrowed it twice now and both times the check engine light has come on. Each time the code was P0519 - Idle air control. Any idea what he’s doing to my car? Or could this be a case of sabotage so he can talk me into getting that VW…
I think it’s a coincidence. I can’t imagine how he could drive that would cause that code to come up. It’s like blaming him for a tail light bulb burning out.
Idle Air control problems are not uncommon for any make of car with miles and age so I would look at this right now as a sheer coincidence.
It’s also pretty easy to make that Idle Air code come up with a simple wire disconnect… 
But, is there is problem with the idle? Is the idle rough, or stumbly? Cleaning the idle air control valve (iacv) air passages with a Throttle Body Cleaner spray could help.
What could improve the situation wasn’t the question, was it? No, the trouble light isn’t related to anybody.
It has idled rough two or three times but these events always followed backing out of the garage to get the mower then pulling back in quickly. I hate to say it but my husband is the one who pulls it out like that and I think those few times he gave it a bit too much gas. After such an event it will get back to normal if you give it 30 seconds or so.
I really have babied the thing. I don’t get the RPMs up very high before I shift - say 3,500. Typically I drive at 2,500 to 3,500 RPM. My husband does get it higher than that so perhaps that is part of it. (I really don’t blame him for this - it’s just fun to tease!) I’ve read comments about the IACV but it seems like that’s not always the fix. Also see a few posts suggesting a vacuum leak. Regardless it sounds like this is a tricky problem to track down, but no one seems to think its a major concern.
Is the IACV easy to get to for a non-mechanical person? I’m handy, but I’ve never worked on cars…
You know, I do have a license plate bulb out in the back. I’ll have to ask my husband about that…
If you want to try do-it-yourself repair I suggest you purchase a service manual for your Impreza. Then you can follow the step-by-step diagnostic procedure for the idle air circuit or anything else you might want to mess with.
Having a service manual really helps you to properly maintain your car. Well worth the money in my opinion.
Try http://www.Books4Cars for inexpensive used manuals.
I think your IACV is dirty or whatever and it’s right on the edge and just so sensitive that a difference in driving style makes it act up.
I think very soon the light will come on for you too.
Lots of short trips, especially just a few feet will promote build up of gunk in the IACV, throttle body and the PCV system.
FYI, when I’m “moseying along” on flat ground I shift my 4-cyl engine at 2000 RPM. I’m in 5th gear by 40MPH.