High idle

[loganmossmusic]

I have a 97 BK, and I started my freshman year at CWU in Ellensburg, WA in September. Since I started I make the ~250mile drive home to see my fiancee and then that same distance back every other weekend or so. Lately, (last 5 or 6 trips) after driving for about 3 hours, I pull to a stop light and I notice I have to hit the brakes a little harder than usual, and that is because it is idling at about 1100 - 1200. I am thinking maybe engine coolant sensor? That would tell it to keep it idling high I would assume, otherwise the IACV? I am looking for suggestions about what to test and try to figure out the problem.

[Huffer]

Try the IACV first. When you come to a complete stop, how long does it take for the idle to drop? Also, if you shift into N while braking, your brakes don't have to do any more work because the engine isn't engaging the transmission. It just feels like it because the revs aren't dropping as fast.

[jey]

Very few people drop their tranny to N when they're braking with an automatic transmission - and if you do be careful not to hit R instead (been there done that).

Anyway, check the operation of your throttle too. If you have a good OBD-II reader you could see if it's returning to true "0" when you release the accelerator. A visual check of vaccuum hoses also wouldn't hurt.

[Huffer]

I thought the 4EAT had a lockout mode that didn't shift you into R unless you pressed in the button on the lever? My 98GT had it.

But, my bad. I didn't realize he was specifying an auto, sometimes my current car (a 5MT) would high rev coming off a freeway and I would shift into neutral, blip the throttle and shift back into (say) 3rd to continue slowing down. This was a very rare occurrence. Maybe 3 times in the 40k I've driven the car.

[loganmossmusic]

I have an automatic, and you are right about the shift lock, it shouldnt go into reverse without pushing the button. Also, when I come to a stop when this is happening, the idle doesnt drop. It goes down to about 1200 if the car is in neutral or about 900 when the transmission is in drive. I havent cleaned the IACV yet, because I dont have any tools here but I was wondering if there is a way to see what temperature the coolant sensor is showing? I am stuck on that idea because of an experience with a Ford Exploder, we tried all sorts of things to fix the high idle and it turned out it just needed a coolant temp sensor.

[jey]

Idle should be 700+/-100 in Park/Neutral with no load, 850+/-50 with A/C on. The temperature gauge the 2nd gen Legacy is a real gauge for the coolant temperature, but doesn't offer a whole lot of precision. If the sensor is dead I think you'd see it pegged one way or the other, or jumping around a bit.

[loganmossmusic]

The idle is definitely higher than that. Also I have read it at 650 when warm and in park/neutral. It must be my IACV, but why would it do it only after driving long distances? Just a coincidence? I think it would consistently do it, but I admit I do not know much about it.

[Huffer]

Hot air can sometimes cause gaskets to expand or expose cracks - your IACV might need a new gasket. At the very least, clean it.