Toyota Repair: P0420 and P0304, 2002 toyota camry, toyota camry

Question
Hello - My 2002 Toyota Camry with 117,000 miles flashed the Check Engine light today. I got the above codes. I had done a Battery change, starter change and Throttle Valve clean up service at Toyota Dealer in last week. Does that have to do anything with the Engine check light. Please advise. I dont wnt to spend more money ont this. The dealer already ripped me last time for the above service. Thank you in advance

Answer
The p0420 code is a catalityc converter failure code. The p0304 is an engine misfire code on the #4 cylinder, this is the most important code that needs to be dealt with first because it can affect catalityc converter operation and eventually overheat and destroy the converter. If the misfire was not there before taking it to the dealer then it could have something to do with what they did and you should take it back and have them diagnose why it's now misfiring.