What is your typical driving environment? City type with lots of stop-n-go or Highway type driving? Is the transmission automatic or manual? When was the last tuneup? All of those play a significant factor.The 2003 Neon gets 22 mpg. 86,000 miles. Runs great. Spec's say I should be getting close to 30. Is the lower miles per gallon I am getting normal?
+1 for good ol copper plugs. I've always had the best luck with coppers, even in my 2gn. I had platinums in one of my 1gn's and it began to run like crap after about 5k. The plugs looked bad but switched back to coppers and thing ran like a charm until I did my yearly plug change (~15k~)Neons require 30k plug changes and use a copper plug (at least the earlier ones did) and ran worse with fancier plugs from my experience.