I RECENTLEY,,WHEN TO THE M,B DEALER,S SHOP FOR MY CHECK ENG,, LITE WAS ON ,, THEY CHECK THE CAR OUT AND TOLD ME THAT I NEED A O2,, SENOR AND A EGR SWITCH,,, O,K SO THEY INSTALL THE PARTS ,, CHK,,LITE WENT OUT,, DOVE HOME THE LITE CAME BACK ON,, SO IWENT BACK THE NEXT DAY THEY RESET MY COMPTER, AND TOLD ME IT WAS FINE ,,LEFT AND LITE CAME BACK ON, WHEN I WENT BACK ,,TIME ,,3,, THEY TOLD ME THAT THEY NEEDED TO RE ,CALABRAT MY COMPTER, BECAUSE IT WAS RUNING .THE CAR AS IF IT HAD NO EGR,,SYTS,, SO THEY DID THAT AND THE LITE STAYED OFF ,NOW BUT THE CAR STARTS WITH A PURGING,, SOUND, PRESSURE GO,S UP, AND RETUNE TO NOAMAL AND BATTERY LITE BLINK,S SO NOW THEY ARE TELLING ME THAT IT COULD BE A BAD PURG CONTROL VALE,, OR,, A,,PRESSURE,REG,, OR APURG ,, VALE CAN SOME ONE TELL ME WHERE ARE THIS UNIT,S LOCATED ON THE CAR SO ICAN TRY REPLACEING ALL 3 ,OF THEM TO SEE 4 MY SELF IF THIS WILL STOP THE CAR FROM SURGING WHEN STARTING IT PLASE....THE CAR IS 1994 S420,, MEL DWYER,,,,

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meldwyer