Getting any trouble codes from your motor?

Might check and see if somebody has tried to adjust your idle using the
screw on the little throttle connection at the intake, possible to
compensate for a problem.

I would consider cleaning the Idle Air Control Solenoid, as my mother's
older Legacy wagon would die at idle until the part was cleaned, and if
you're already doing a tune-up, maybe replace the PCV valve too.  My Impreza
set a trouble code for the Idle Air Control Solenoid before I ever had
noticeable problems, but cleaning the carbon build-up from it with some
carbeurator cleaner to free up the little air valve cleared the trouble
code, so all is happy.  On my last tune-up, I cleaned it on my XT6 as well.
They all seem to be pretty much the similar, so I doubt you'ld have too much
troubles in pulling it out and cleaning it.

When I pulled the solenoid that was setting the code, I noticed I could
rotate the valve slightly with my finger and that it would stick, open,
closed, wherever I put it, but after cleaning the majority of the carbon
out, it bounces freely back to it's centerpoint as I would figure it should.
(-;

I dunno if you want to use carb cleaner or not, as I couldn't say what ill
effects it may have to downstream sensors/ components, but it worked for me.
I tried to be sure it was reasonably evaporated before reinstalling the
solenoid and starting the engines.

I considered just replacing the solenoid on my Impreza, but the parts guy
quoted me into the $800 ballpark for it.  Needless to say, I didn't bother
asking about the solenoids on the other two cars.

~Brian