sunfire burning too much

[twistable_deer]

Hello, I have a 2002 sunfire gt coupe and I have a problem with the car burning too much fuel. I drive to school everyday which is about 100 kms there and back. I never turn on the a/c, I never roll down the windows, I don't do any hard accelerations and I use cruise control as often as i can which is about 80-90% of the time. I don't put any cheap gas in (no name companies) and my car is burning about 11 liters/100 km highway. I drive almost 95% highway when I drive to school between 100-150 km/h. I replaced the fuel filter and I just changed the oil (synthetic) and I also installed a new air filter (about a month ago). I had removed the air intake manifold and cleaned out the intake ports which made my car burn less but still a lot. I removed the spark plugs and they where somewhat white so I cleaned them and regaped but the gaping was fine. I took a flashlight and looked down in the cylinder and indeed the cylinder looked wet and there where carbon deposits on the top of the cylinder. I don't believe that my car is burning coolant because I have never filled it or had any white smoke coming out of my exhaust pipe. I do have a code which is an evap code which I have to fix before November for an e-test but I had the code ever since I bought the car which was about four years ago and the car burned perfectly. As I was testing my 02 sensor's via the scanner and the live data function. I let the car warm up and i revved it to about 2,100 rpm which is when the 02 sensor's work the best and i was getting a reading of about 0.6-0.9 volts so I think that the car knows it's running rich but it is not doing anything about it. What do you think the problem is and how do you think I can fix it?

Thank you

 

[melsg5]

Your are driving to school doing between 62 and 93 mph and are getting about 21.3 mpg. You dont state how much of the driving is being done at 93 mph which would significantly lower your gas mileage. Are you sure you only have the evap code? Have you done a compression test? Have you tried setting the cruise control to 100kph and not going any faster? For an automatic the EPA rated the car on highway at 26 and a manual 29.