1997 MERCEDES 280

CAR STARTED TO MISS, UNDER ACCELERATION. IDLES SMOOTHLY PRESS ON GAS AND IT JERKS. HAVE HAD TUNE-UP $600+ LOCAL GARAGE. HAD TOWED TO FOREIGN CAR SPECIALIST SPENT $750 LEAKING COOLANT LINE AND A KNOCK SENSOR. HIS COMPUTER SHOWS NO FURTHER PROBLEMS.
HE WANTS TO TRY A THROTTLE ASSEMBLY BUT IF THAT'S NOT IT, THERE GOES ANOTHER $7-800 SPENT. COULD IT BE SOMETHING IN THE FUEL, INJECTORS? INJECTOR CLEANER AND FUEL FILTER, NO HELP. DO I HAVE IT TOWED TO MERCEDES GARAGE AS THEIR DIAGNOSTIC WOULD BE MORE CUTTING EDGE OR MIGHT YOU HAVE AN IDEA OF WHAT ELSE COULD BE CAUSING THE MISS. IT IDLES JUST FINE, IS IN GOOD SHAPE, USES NO OIL ETC.