Hi, I have a '04 WRX that had a high idle problem for a little while today, and the fact that it went away has me stumped, and making it a pain in the ass to diagnose. I'm pretty experienced with working on cars, but this stumps me... the fact that it went away on it's own. I guess that rules out anything physical like a vacuum leak, so I'm thinking maybe the computer was causing it? Today was the first time it's ever happened, but I want to figure this out because it's bothering me, I keep my car in perfect condition.
I was on the parkway today, car running perfectly fine as usual. Then I got caught in a traffic jam (something I experience multiple times a day here, so nothing out of the ordinary for my car). It was an accident that just happened, so it was dead stop and go for about a half hour. After about 10 minutes in the jam, my car started to idle high. It wouldn't drop below 1500rpm. If I revved the engine, it would drop back down to normal for a second, but come back up again. The gas pedal was being VERY sensitive to revving it too. I pulled over and checked for any disconnected vacuum lines, but all was good. I also made sure my floor mat wasn't catching on the accelerator pedal and keeping it from coming back all the way... that's happened to me with other cars in the past.
This was particularly annoying because as everyone here knows, these Subies don't like to shift into first unless your input and output shafts are matched close enough. Well of course, since it was idling at 1500, it was being a ***** to shift from neutral into first, something I had to do about 300 times during the traffic jam. I had to keep muscling it in. I was getting really pissed off, since I was beating the hell out of my syncros and there was nothing I could do about it.
Once I got moving again, it was annoying to upshift, because the RPM pretty much stayed steady every time I clutched in. But then after about 2 minutes of driving, it went back to normal. I haven't been about to recreate the problem.
Wild guess: could this possibly be from overheating? I did notice that it felt hotter than normal under the hood when I opened it. Would the computer raise the RPM slightly in order to circulate more coolant if it's overheating? I was driving on the highway for about 20 minutes, then came to a stop and go situation. Shortly after, it started happening. That would be the ideal time to start overheating. Then after moving for a little while the problem went away, which would make sense, there being more air coming through the radiator.
The thing is, my temp gauge was reading perfectly normal, and the fan was clicking on and off like normal, not staying on like I would expect if it was overheating. And it wasn't overly hot out. It was in the evening, around 55-60F. The only thing that makes me think overheating is how it felt when I opened the hood... other than that there are no signs that point to it.
Unless I'm in the far fetched situation that my radiator fan isn't moving as much air as it should, I ended up in the perfect condition to overheat, and my temp sensor is defective, all at the same time, I think it's not the likely cause. But that's the best guess I could come up with.
Has anyone else had this happen to them and can offer any suggestions?
BTW: the car is completely stock, except for an Injen air intake (I know, I know, but it was already in the car when I bought it ) I know air intakes have caused trouble with these cars in the past, but I think this is one of the few that works well with the car, since it's always run perfectly fine with it. It's the same one that's sold on fastwrx.com, who assures that it doesn't mess with the air/fuel readings.