2005 Ford Taurus I Keep Getting PO300.

Alright so I have a 2005 ford taurus 3.0. 6 cylinder 12 valve. I changed the spark plugs, coil, Gas Filter, EGR Valve, PCV Valve. After the change of the EGR Valve the light went off after that it was off for 2 and a half months than out of no where when I was driving the car the light came back on I could not believe it. So we took the diagnostics scanner for codes and saw PO300. Right now we have no light and we keep seeing PO300 on our scanner one time than we take it out for a drive check the scanner and its gone. We recently cycled through the emissions test once again and its still doing the same thing with PO300 its shows up on the scanner than disappears after a drive. Could anyone explain this to me if the car needs live data or give us any information on what could be causing this annoying code. Also I would like to State the car runs fine no bad Shaking when we drive or just idle it in general.