Help Misfire And Engine Code P0303 And P0300

[tooredhots]

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!

[GuyTelefunken]

Although I don't have any advice for your problem at this time, I am curious about your previous ECU replacement.

What was the problem in the past that required the ECU to be replaced?

[lenore]

When you took the coil packs off, maybe one of the wires is broken at the connector or internally after disturbing it. Look very closely at the connectors. Also the Coil pack connection to the spark plugs, look for signs of arcing. Sometimes it helps to put dielectric grease on the connection to prevent any moisture and possible arcing. Please note also dont use Bosch plugs, they suck bigtime and act exactly the way you discribed your failure. NGK or Nippondenso only.... Look very close at the wiring to Piston number 3....and the cops for arcing.