I've got a 2004 Forester XT with 13000 miles on the odo. I just got the car back from having the rear differential replaced. I noticed that the idle seemed even rougher than before...and it was never particularly smooth. When warm, at idle, the tach will fluctuated every 5-10 seconds between 500-1000 RPM. And every once in a while it will actually stumble and go down to about 250RPM and almost stall out, with a bit of a shudder. The idle is erratic enough it will actually jangle the keys in my ignition at a stop. It does not just correspond to the AC compressor cycling.
I can't say for sure that it changed right after the rear diff was replaced but it seems like it to me...but my wife disagrees...she said it was just as bad before the service.
I'm obviously back to have it serviced...I've owned the car for 6 months and I'll already have had three days in the shop with four service trips so while I love the car I'm not enthused about Subaru reliability and can't see myself getting another one. :x I hate to think about what will happen if I start modding the car like I want to...the dealer will say everything is a mod problem.
Anybody out there with an erratic idle on a new XT?