i just changed my motor in my 90 legacy. my new(used) motor already had all the sensors on it. when i first fired it up the idleing was jumping from 3500 down to where it would almost stall. then it would jump back up and do the same thing over again. i got a code for the iac valve so i swaped the one off my old motor onto this motor. it now idles smoothly but it idles at about 1200 rpm when warmed up. how do i get it to idle back down to normal?? i'm assuming it has to do with the iac. is their an adjustment on it. i did notice that it has 2 screws on the top and it looks like i can rotate the valve. so anyone have any ideas?

Is your car AT or MT? There are different IAC valves & other sensors for the AT & MT equipped cars.

 

Does the new motor's throttle body have a screw on top of it?

http://main.experiencetherave.com/subaru/images/tb/

 

If it does, turn that needle valve counter clockwise slowly until the idle comes down.

 

Typically you don't want to mess with adjusting the IAC valve because it comes "calibrated" from the factory. I ran into a similar high idle issue on my 90 Legacy, and it turned out to be that throttle bypass needle valve screw. The engine cover hides it very well, so I spent a lot of time troubleshooting the problem. The high idle occurred due to me cleaning the throttle body and removing the "sealant" that was in the throttle body between it and the throttle plate.

my car is an AT and the engine i put in was from an AT car also. i'll check for that screw. i didn't really take notice if their was one there or not

Ok, yeah let me know whether you have that bypass needle valve.

it has it but the bracket for the top cover is blocking it. lolwayoks like i'll have to remove 2 of the bolts for the throttle body to remove the bracket. i did run the car and the idle did seem to be a bit lower than it was. went from 1200 to about 1000. so i might run it some more and see if it changes. this motor was setting around for a little while. if it comes down to it i can always just swap my old tb back onto this motor

Yeah, the bracket blocks it, and is why I missed it initially as well. I spent a lot of time troubleshooting why I had such a high idle, then found that screw.

Did some of the early 90's eras have a solenoid valve on the throttle body that it would open to let in extra air when the a/c kicked on or something like that?

Did some of the early 90's eras have a solenoid valve on the throttle body that it would open to let in extra air when the a/c kicked on or something like that?

 

Thats what the IAC does.

 

Any CEL on?

Did some of the early 90's eras have a solenoid valve on the throttle body that it would open to let in extra air when the a/c kicked on or something like that?

 

No they didn't. To the best of my knowledge, that needle valve on the throttle body was a way for the factory to fine tune the air bypassed through the throttle body. On the later models, 91 or 92, the needle valve is no longer there.

ok i turned the screw in 1 turn and it seems to have fixed it. so i'll drive it some and see what happens.