My wifes car keeps throwing several codes randomly ; a 170 Fuel trim left bank and also egr code and then it will show a double code for the cats not working well enough . And sometimes it just says missfire on #1. I am a fairly good mechanic with good understanding of most automotive stuff but these codes are driving me bats. Spark plug wiring is brand new and supposed to be better than stock . I had to do the Starter change and was really pissed when I found where it was and all I needed to tear down to get to it . All went back together OK but these codes started after that . Could the cats need replacing ? Car has 158000 mi. and we never use "junky" fuel .

And by the way " Thank you " because I could not have made that starter change without " Forum knowledge "