When in gear (ex. Reverse, Drive, 2nd, 1st) my car idle "settles" around 750 on the tach, but then starts to fluctuate around there, moving up to 900(or so) then dips down to about 500 on the tach. While the idle speed is fluctuating my voltage drops dramatically. It will go from about 14 on the volt meter down to about 9, but not in the red - 8 on the volt meter. I recently replaced all the plugs, fuel filter and a casket on the #8 exhaust port, new oil filter, and a voltage burn-off relay. I am torn between whether it is the Mass Air Flow sensor, the Throttle Position Sensor or the Oxygen sensor. If anyone has ANY information about this type of a problem please contact me.