Just bought a 2000 V40 with 83k miles. Picked it up yesterday in Philly and drove 275 miles back to Pittsburgh. It ran just fine yesterday but today it was idling rough and the check engine light came on. I'm gonna take it tomorrow to the mechanic and have them scan it see if any codes come up. Anybody have any thoughts as to what might be causing the rough idle??

 

i had the same problem with my 98 v40 and the problem was the egr valve cleaned it out with carby cleaner and Subaru top engine cleaner but the valve back in and car idels at 850 before it was 1200 and i dont have an engine light display any more apparently because of the rough idel it was throwing the o2 sensor out of wack but all sorted know
hope this helps