What can cause a 2008 Chrysler Sebring 4 door burn toomuch gas?

Most likely an 02 sensor. Another thing to check for is a plugged up catalytic converter.

Also remember letting your car idle for more than a minute is worse than driving 100 mph. The slower you go, the more gas it burns. Your engine could also be suffering the effects due to the addition of Ethanol to our gasoline.

That is a fact ethanol is bad in every way. If you are burning ethanol try non-ethanol and then recheck your mileage. Factoid......it takes 1.4 gallons of gasoline to make 1 gallon of ethanol.

Will it hurt my car by putting no ethonal in?

On the contrary it will help to not run ethanol. A little blurb about ethanol. Ethanol has finite shelf life. This is in part because it attracts moisture similar to the winter time additive you use in the gas. Ethanol will attract moisture from anywhere it makes contact with it including the air. Point being when you burn ethanol you are putting extra moisture in your fuel and engine. This causes corrosion in critical parts like injectors, pumps and sensors. Many car manuals advise against using ethanol. Here is one of hundreds of articles showing the damage ethanol is doing to engines. http://www.businessweek.com/lifestyle/content/may2009/bw20090514_058678.htm