I have a 2005 S60 that I keep in great shape. I've taken a lot of good advice I've received on the forum. I just put on new tires, new plugs, and a new gas filter. However, my car when first starting was hesitating a little bit like it was trying to breath or something. A few times, if I didnt give it gas, it would die. That's why I put in new plugs and a fuel filter. The car definately ran better and I could tell a difference in performance. However, I am still getting that hesitation. A friend of mine suggested I go to a parts store and buy a fuel injection cleaner. He also suggested that maybe every 3rd or 4th fillup I put im premium gas. Please help me. Is this advice valid? I also jusyt replaced the air filter.