When I first got it the Neon would idle rough at every stop. Seams to be smoothing out. MPG is improving as well. First tank got 23.7mpg, filled last night and it is up to 25.3. Think I will run a couple more tankfulls and add some cleaner. Don't want to loosen up too much too quick and clog something up. They were rated 25city 32hwy. So already in the ballpark. I rarely even made the low end of ratings with the Magnum. Was usually around 17-18 Made 20 for a short time with new plugs