[wiswind]

The Idle Air Control valve (IAC) may have gone bad again....The most common cause of idle problems as it controls the air (and thus the idle) whenever your foot is off the accelerator.
You could try removing it and spraying a small amount of "Sea Foam" into it.

The other possible cause would be the Throttle Position Sensor (TPS)...which is mounted on the side of the throttle body. As the name indicates, it senses the position of the throttle.....as in the position of the accelerator......
Oh.....most likely not your problem....but I have had the accelerator pedal catch on the floor mat.......