I recently removed my '03 gls spark plugs out of curiosity and inspected them. They are OEM NGK plugs and only 60,000 miles old. They were not bad, but I cleaned them with copper wire brush and sand paper. The gaps were much wider than the original setting, so I regapped and reinstalled. After fill-up, I drove over 300 miles, but still there was gas left around 1/3 of gas tank. I calculated mpg after fill-up again. Wow! What a difference! It was whopping 37 mpg. I have never had such mpg. I used to have around 30 mpg from the day 1. I don't think I need to buy a new car now. You know what? My odometer hit 310, 600 miles today. I use synthetic oil and check tire pressure weekly and I think these help save gas, too.