I am on my 4th tank of adding 100cc of acetone in my 98 neon and it made a big difference.The car has 100,000 mi. and is not maintained that well.I can't remember the last time I changed the plugs!THe car used to ping and rattle and had a slight miss that I thought was a bad coil.Now the piece of crap runs like a top.Haven't measured the mileage but can tell its better because iam getting couple more days out of a tankful.The idle speed has increased to the point I need to do something about it,but don't know how to lower it(I know nothing about computer cars!)If someone can tell me how to lower the idle speed I think the car would get even better mileage.Anybody out there know how to adjust idle speed on a 98 neon single cam?The only thing I know how to do on this car is change head gaskets!