I recently bought a 2003 cavalier as a gas saver car. it has 104000 miles on it but it still looks good and runs good till about two weeks ago. my rpms started to bounce from between 600 to 900. i decided to clean the throttle body with gumout carb cleaner and removed a bunch of carbon build up from it. i thought it would help but instead it made it worse now my car started to idle at 1500 rpm and would jerk when i would be driving on the freeway and would start to slow down or when i turn the a/c on. i started fixing it by replacing the IAC and IAT sensors and gauging for a vacuum leak but none was found. i had code P0507. i took my car to a mechanic and told me that the jerking could be due to bad gas so we changed out the fuel filter and had a lot of black gunk shoot out. the filter was so dirty that you couldn't even blow through it. doing that it made the rpms come down to 1000 at idle. need help don't know if i need to change the fuel filter out again or if it may be something else. what can i put in the gas tank to clean it out? what can make the car idle high? what should the idle be? by the way it an automatic trans can it be anything with the trans? please help