01mazda mpvcodes p0421&p0300
 

have had plugs wires replaced and sensors indicate good.catalyctic im not too sure of.has anyone had the same thing and it not be the catlytic converter,i also know these codes indicate misfire even multiple ,i dont under stand jus got out of shop ,had one sensor replaced ,repair said others were okthey had a newer diagnostic tester that could test seperate things to pinpoint,is ther such a thing or am i being taken for a long ride on a shrt pier??it coded prior to this repair stateing catalytic possibilities,although no misfire code,did code months ago and was told try a tuneup,which i know it did need.was told bad sensors could cause prob,,,also was told sensors are what pick up catalytic problems so sensors must be ok,if its catalytic converter then ill just have to fork out and have it done as well,but has anyone ever had this same codes and it be somthing totally diffrent,,,what on earth could cause misfires,,,had plug in wires and tune up done,,,could it possible be coil pack
causeing misfire,,,one last thing i was told there is away to test catalytic converter by it self to see if it is that in fact,,,need answers,,,if youve had same prob and codes please let me know,,,i know repairmen or mechanic love it when you have no idea,,that way they or not all but some can milk you dry,,,needing info please