Hi all. I have a 2005 G35x with about 128k on it. Yesterday I was changing my spark plugs (Mind you I have never changed plugs before but seems simple enough right?) and I guess they weren't correctly gapped so my car was misfiring and I was getting code P0300, which is random/multiple misfire. So I put the old plugs back in and they were still misfiring. I could not figure out why. Unfortunately I had to drive the car about 2 miles like that back to my house until I stumbled upon a post on here which made me realize that my coil wires may have been mixed up (Which they were, back and middle plugs on the driver side). So I fixed that problem, and my car was running good again. Today, I turned my car on and the engine light came on with a P0430 code "Catalyst system below threshold". I cannot figure out what is the exact cause. I dropped it off at a local mechanic today, but I won't know until tomorrow what is wrong with it. Anyone have any ideas? I was running white smoke thru my exhaust while I ran the car with the misfire, so I was thinking that maybe my o2 sensor on the driver side were dirty or damaged from the smoke passing thru it.

 

Either an issue with the cat or the sensor. I'd clear the code and see if it comes back, no need to jump to conclusions