Clogged cats can affect the entire engine including ignition systems. Some clogged cats have gone as far as to create detonation from extreme back pressure, causing catistrophic failure.

I'm glad plugs were your fix.

 

Well I knew I was ok cuz even with 3 codes I raced another GT and left him behind lol:-) And cats didn't rattle... But I'm all good now. Can't believe it's over!

 

How's your long term fuel trims now? +20% at idle is high.

 

After driving about 25 miles I got +12.3 +14.8 with STFT ~+-.8 on both banks... It's usually the same when I'm cruising highway too...