Recently did a tune-up on my 04 ZTW, when looking up Seafoam I found one thread that said to run 1 1/2 cans in the gas tank and 1/2 in the oil. Drove it for about 250 miles then did a second oil change, as well as replacing the fuel filter. The plugs were barely a pin point where the center electrode should be, so installing the Autolite 103 coppers made a noticeable improvement, though the car was not running badly before. My issue is this, my fuel mileage is very reduced. While not a sound way to calculate mileage on a tank of gas, I generally got around 125 miles at 3/4's of a tank and between 190 to 200 at half, usually getting close to 300 at 1/4. My mpg was pretty standard at 26 to 27 for the driving that I do to and from work. While running the Seafoam I was at 80 for 3/4's and 135 for 1/2 a tank, on the second tank since I am at 115 for 3/4's and was at 168 just above 1/2 a tank. My son used the car over the weekend and at close to 1/4 of a tank it is at about 230 miles on the trip counter. I am going to look at the pcv valve and see if my neighbor can help do a compression check. I just don't understand that my mpg went down after running the Seafoam. I did put 89 in this last time, so I will run to empty and fill up on 87 again, I just don't know what happened. I plan to clean the maf tomorrow. Any feedback is welcome, I am also looking over the site for any hints about where to look and what to do.