When I bought my car it had 250miles on it.. It has always had a rough idle.. At a red light I put one foot on the gas and the other on the break.. As soon as I hit 550rpm or maybe 600 the engine smooths out.. If I don't do that I hear this weird (I'm not sure the best way to explain it) but a whining sound that goes up and down like the engine doesn't have enough power... another problem I see, if I don't keep the RPMs around 550 - 600 the fan kicks on more often and I see my headlights and the interior lights dim a little.. the car drives great once I accelerate.. and there seems to be no loss in power... I also think it could be the gas I use (Moble Premium) 10% ethonal.. but, I'm not sure.. It seems every station here in South FLA.. has 10% of ethonol added to the gas.. I just did an oil & filter change (moble 1 0w40) and put in some Cheveron injector cleaner.. but it doesn't seem to affect the idle..