I have a 2002 blazer xtreme, with the 4.3 V6 Vortech engine. About a week ago it started idling really rough and didn't really act like it wanted to go from a stop, it seems as if a single cylinder is misfiring, which is why some suggestions people have made don't make sense to me such as certain sensors or the fuel filter because wouldn't these effect the whole engine and not a single cylinder, I may be wrong about this but if you have one of these suggestions could you please explain it to me? The idle is worse in gear than it is in park. At high revs it would clear up, however when I press the gas pedal the engine makes a squalling noise and we were unable to determine where exactly it was coming fron. The past couple days it has been dropping in rpm while I'm driving around 65+, this feels as if the brakes is being lightly tapped while I'm driving. Also it doesn't seem as if the car wants to accelerate at times until I press the gas pedal down pretty hard then I will have an rpm spike and then the car will accelerate. Gas mileage is also worse then normal. I did a tune up with wires, plugs, cap, and rotor. Changed the fuel injection spider. Changed pcv valve and cleaned MAF sensor. Ignition coil was changed as well. Oil and transmission fluid and filters were changed a couple months ago and are not out of date. Air filter isnt clogged. Throttle body looks fine however my gas pedal doesn't feel exactly smooth when pressed down anymore. Issue does not change with heat or air on, and it also doesn't change whether radio is on or not and doesn't cause the radio to lose power. Check engine light is on but has been almost since the time the car was purchased new, however it does flash now when accelerating, it doesn't flash a certain number of times, it just flashes continuously while gas pedal is pressed. I have not been able to find a solution to this anywhere and it has quickly become somewhat expensive for me. I believe this is everything I can think of at the moment.