So I had some stumbling at idle a few months back and cleanded the IAC valve with great success and then the car ran like a champ BUT it is now getting bad again after 3 months. Why is this happening?

 

Is it blow by causing this? Car has 190K KMs on it and seems to run great still with lots of power.

I've got the same problem. Your IAC might be going bad. I really need to replace mine, my cold idle is non-existant!

the pcv valve dumps a misty oil blow by back into the intake.....and I guess just normal operation causes them to get gunked up.

NT

ehh....it won't fix how the pcv system works. It's just that way... Only thing you can do is put a catch can from all the breather vents before they go back into the intake track. Other then that....keeping the oil from the breathers is a lost cause.

and with that many Ks it deserves a bit of wear. A lot of other engines would already be dead.

I would just plan on doing a cleaning every few months as long as you plan to keep the car.

Erm, Josh...the Subaru PCV works "backwards" compared to most others. The PCV valve draws straight from the crankcase, pulling fresh clean air - ahhh! - through from the valve covers. My point: A catch-can/oil-separator would only be needed on the hose that connects up to the PCV valve.

I'll have to take a look at the pcv diagram.......I think I remember it acting different depending on how much vacuum you have or throttle position.