My 07 S60R M66 has a random rough idle on startups. It only happens every week or two. I daily it to work, if it's going to happen it's almost always in the morning and if it doesn't clear itself up within a few seconds a slight rev or two sets it straight. I've had a couple times where the rough idle persists through driving and the car sounds like a crappy WRX going down the road. I replaced the fuel filter, which looked like it could be the original, and the problem only slightly decreased in frequency. Recently, after driving for 15 minutes with no problems, I was accelerating in 3rd and there was a sudden loss of power, it started idling rough, and the check engine light started flashing. On the next startup everything was fine. I've seen things on checking the PCV system, MAF, coils, injectors, spark plugs, and even saying it could just be bad gas. Only code my subpar code reader picked up was a P0300. Looking if anyone else has had an issue like this before I start digging in.