I WAS DRIVING ON THE FREEWAY WHEN MY ENGINE LIGHT COMES ON, WHEN I PURCHASED 1990 LS400 THE PREVIOUS OWNER JUST RECENTLY CHANGE THE OIL, THE NEXT OIL CHANGE IS 189500, THEN CHECK ENGINE LIGHT COME ON AROUND 189100, SO I CHANGE THE OIL AND RESET THE COMPUTER, BY THE WAY I STARTED USING SYNTHETIC...