Hello all- I’m a new subscriber and I’m hoping someone can steer me in the right direction as what steps to take with my car. She’s a 2004 g35 coupe and she’s been awesome for the five years I’ve had her. She has 250,000 miles, and has a valve cover leak and a crankshaft front seal leak, which I’ve been aware of for a couple of years. I regularly checked my oil levels- with a hard to deal with dipstick, mind you- and averaged adding 1to 2 quarts between oil changes. Last month I noticed she began riding tough- seemed to be surging- and also a rough idle. Checked obd codes and I got 4 codes. P1031, P1148, P0303, P0037. I had her towed to a dealership that has a service department. The car would still run but I didn’t know how serious of a problem I may have so I chose to have it towed. They repaired the 02 wiring and did a tune up. Also put a new battery on (?) bc they said it was having trouble starting which I had noticed in the past but thought it was a bad connection between battery and port. I had new spark plugs put on in 2-2020 but anyway they replaced those. They informed me of the oil leaks but I chose not to have that repaired since my bill was already 1200.00. I also had two tires replaced and a hub assembly repaired. When I picked the car up there were no misfires felt during normal driving. It would still surge a little during idle, but not as it was. Well three days ago it started doing the misfiring again. I called them and they said it could be oil leaking onto spark plugs, fouling them out. I asked about the coils and it was as if they were never checked although I don’t see how they could not have been. And I wasn’t told if my old plugs had oil on them or not. So here I am again, not driving my car and wondering what my next step should be. Thanks to anyone who can give me any input

 

Misfire on these cars is usually a bad coil pack or a spark plug.

Looks like your main OBD code that is causing the misfire is P0303, which means a misfire in cylinder #3. The rest of the codes are just there because the engine isnt running right and throwing off the air/fuel mixture.

So change the coil pack on #3 cylinder and see if the misfire goes away. Inspect the spark plug too while youre at it.

Btw cylinder #3 is on the passenger side, in the middle. Heres a pic for reference:

 

Scorpio pretty much spelled it out for you.

I would add check your spark plug tube seals to see if you are getting oil dumping into the spark plug tube. If those are leaking, replace the cover and it’s seals with oem ones as the oil leaking in the tube will cause misfire.