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I recently changed my spark plugs on our 98 gs300, the car has 150k. It ran fine for 100 miles or so after the plug change. Then it started missing, and gave a code p0303. I have swapped coil packs around put the old plugs in, replaced the wireset, in many different combinations. To no avail. Can anyone offer any suggestions before I take it to the dealer? The ecu has been replaced once before. at 90k. Thanks in advance!