97 Legacy 2.5 High Idle when Cold

[G-Strad]

Hello All

First post here and need some help. The GT has 97K miles and runs really well. The problem is cold idle. When first started, idle settles around 1500 but goes up when driven. This is a MT car. Driving a short distance and then stopping at an intersection produces an idle around 2500. This will continue until engine gets a little heat in it. Until then, when the clutch is in, it will rev back up to the 2500 range. When warm, not even fully, the idle will begin acting "normal". Occasionally, it will be very slow in dropping down to the 700 idle range. I have replaced the plugs and wires and cleaned the throttle body. Could this be coolant temp sensor related or IACV? Where is the IACV and how is this checked and cleaned? Location of temp sensor? Any other thought? I have read about the IACV for 2.2 engines but haven't found 2.5 yet. Any help would be appreciated!

[Legacy777]

Has it always done this, or are you just noticing this behavior recently?

 

It sounds pretty normal.

 

The coolant temp sensors are under the passenger side intake

http://www.main.experiencetherave.com:8080/subaru/images/injectors/DCP_2477.JPG

 

You'll only have the one bigger one.

 

If your IAC valve is the newer style it's right at the throttle body. If it's the older style, it's off to the passenger side of the intake manifold.

[G-Strad]

It has always idle high when cold but not this high and not for this length of time. It will sometimes idle very high even when warm but will slowly drop down to normal idle speed at a stop, it just takes approx. 20-30 seconds. When first started, it will idle around 1500, then after beginning driving and while still cold, it will idle 2500+. Watched it this a.m. and this is how it behaved. Once it had some temp in it, it slowly began dropping the idle back until normal. Could this be the temp sensor? Thanks for the help.

[Legacy777]

It could be a temp sensor.....usually the temp sensor causes other drivability issues.

 

You may want to look at cleaning the IAC valve.....and/or if you want, replace the coolant temp sensor.

[G-Strad]

Thanks for the help, Josh

 

I looked for the temp sensor and the only one I could find was at the top/front of the engine. Looked like a traditional temp sender. Couldn't find any other sensors on the passenger side. Might need to look further. I believe I found the AIC valve. There appears to be a small line coming from the throttle body to the valve. The the small hose comes out the other side of the valve. There is also a large hose that goes to the air intake plumbing. On top is a solenoid that has slotted adjustment holes for the screws. Am I correct that this is the AIC? On the passenger side next to the TB. Short hose connecting the two. Can you give me the procedure to remove and clean valve? Will I need a new gasket? What should I look for when removing the valve? Back to the temp sensor. Where would it be in relation to this valve? Thanks again for the assistance.

[ninjaben43]

sounds like a normal wear and tear issue, i have the same car. when subaru switched to a ecu controlled auto choke, for the mpfi, they tried to keep it similar to the traditional carborated version from older styles, due to having all aluminum engines it is wise to have a higher rev when warming up so oil can pump faster, reducing any scaring to the cylendars etc. when your sensors get well used they start putting out false (only by a little) readings. thus, giving the ecu the impression that it needs to adjust the fuel to air ratio, or inccrease or decrease the timing. the same thing happens at high altitudes. i would suggest cleaning all of your sensors one at a time that read off the engine, chances are you would notice a difference even without a problem. even so, probobly eliminating it.

[G-Strad]

Can you tell me which sensors can be cleaned and what should be replaced? Also, can you point me in the direction of the temp sensor? I tried to find the one from the earlier post but, no luck, just saw the one I responded to above. Any other maintenance items I should be checking?

  ninjaben43 said:

sounds like a normal wear and tear issue, i have the same car. when subaru switched to a ecu controlled auto choke, for the mpfi, they tried to keep it similar to the traditional carborated version from older styles, due to having all aluminum engines it is wise to have a higher rev when warming up so oil can pump faster, reducing any scaring to the cylendars etc. when your sensors get well used they start putting out false (only by a little) readings. thus, giving the ecu the impression that it needs to adjust the fuel to air ratio, or inccrease or decrease the timing. the same thing happens at high altitudes. i would suggest cleaning all of your sensors one at a time that read off the engine, chances are you would notice a difference even without a problem. even so, probobly eliminating it.

[Gnuman]

  G-Strad said:

Can you tell me which sensors can be cleaned and what should be replaced? Also, can you point me in the direction of the temp sensor? I tried to find the one from the earlier post but, no luck, just saw the one I responded to above. Any other maintenance items I should be checking?

 

From the position that you found that sender in, it sounds like the Oil Pressure Sender, not the temp. There is one sender located below the intake manifold, on the passenger side, on a flat pipe that sits just above the actual block (Josh, I know you have a pic, could you help us out here?). If you look under the throttle body, on the passenger side of the car, right in front of that big hose (PCV valve), you should see it.