Hi everyone, I have a 98 Camry that recently had the check engine light come on. At first the car seemed to be running fine, but lately it has been feeling very sluggish. The first time the light came on the codes were PO302 and 303. I changed the spark plugs and wires and the light turned off briefly, but the car did not run any better.

The light came on shortly after. Now the codes include:
PO300, 302, 303, 420, and PO171.

What could be causing the misfires? I was thinking the 2nd and 3rd cylinder ignition coil, but didn't want to change anything until I had a better idea of the problem.

Recently I've noticed an exhaust leak, despite having the entire exhaust replaced about 2 years back. Could this be causing the Cat problem or is there possibly unburned gas clogging up the cat? Any other possibility?

I'm not really much of a car expert, but I am a college student without a large income so it wouldn't be possible for me to spend thousands at a dealership determining and possibly solving the issue/s. I hope somebody here can help me out in determining the cause of these problems and perhaps give me some guidance as to how to get these fixed. I appreciate any help you can offer. Thank you.

 

A misfire can cause the P0420 code.

You can swap coils with another bank and determine if the codes change.

Where is the exhaust leak, if before an O2 sensor this can cause problems.

Might clean the MAF (if the engine is the V6).