4.6 liter surges/rumbles

HOWDY! MY WIFES 2000 GT CONVERTIBLE HAS AN UNDIAGNOSED PROBLEM: AT IDLE (COLD OR HOT) IT WILL OCCASIONALLY "SURGE" (E.G. ENGINE REVS WITHOUT THROTTLE INPUT, ENGAGING THE TRANSMISSION & REQUIRING ADDITIONAL FOOT PRESSURE ON BRAKE TO PREVENT TAKE-OFF AND FLIGHT! ALSO POSSIBLY RELATED: DURING DRIVES AT VARIOUS SPEEDS CAR WILL START "SHUDDERING" (MY WIFE CALLS THIS A RUMBLE) - THIS CAN BE CURED BY EITHER HITTING THE GAS OR TAKING OUT OF GEAR AND TAPPING THE THROTTLE.
ALSO: "GHOST CODES " ARE OCCASIONALLY THROWN TO THE CHECK ENGINE LIGHT (NOTE: INDEPENDENT CERTIFIED MECHANIC SAID TAKE IT TO FORD DEALER & FORD DEALER SAYS THEY ARE "GARBAGE" AND NOT REAL CODES AT ALL - ALL HAVE TO DO WITH OXYGEN SENSOR - BUT THEY SAY THAT FOR OXYGEN SENSOR TO BE BAD, THE LIGHT HAS TO STAY ON WHICH DOES NOT HAPPEN.
I HAVE HAD THE AUTO TRANSMISSION CHECKED & IT IS A OK.
THE MECHANIC SAID HE COULD NOT FIND THE PROBLEM.
YESTERDAY, THE FORD DEALER SAID THAT THERE IS NO PROBLEM - THAT THE "AIR-CONDITIONER" CAUSED THE SURGING AND AND SHUDDERING. HOWEVER, WHEN DRIVING IT HOME , IT STILL DOES THIS WITH THE AIR OFF.
THE DEALER SAYS THAT THE OXYGEN SENSORS, FUEL INJECTORS, COMPUTER, IDLE SPEED SENSOR, PLUGS, FUEL FILTER, AIR FILTER, EMISSIONS VALVES, ETC. ARE ALL IN TOP NOTCH CONDITION.

DONHEF

Thanks, i will have the dealer check the DPFE. That is the one thing which I don't believe was checked.
Appreciate that ! And my wife's Dark Metallic GREEN 2000 gt convertible with chromed GT mags and black top with darkened windows appreciates it even more than I.