I've been having issues with my 2003 G35 lately (rough idle/misfire) and I was able to hook a code reader up to it. It gave me the code P0303 Cylinder 3 misfire. I've already changed the spark plugs (which were incredibly bad) so I know that's not the issue. I've ordered a set of coil packs but are there any other possible solutions that I should know about if it's not a spark plug/coil pack issue?

 

Try swapping the coil packs and see if the code jumps.

Fuel injector/delivery, vacuum leak, etc... Start with the basics and then go from there.

 

Swap the coil packs around and see if the code changes to another cylinder.

Other causes could be a clogged fuel injector, or bad oil leak, or loss of compression. What did the plug look like from that cylinder?

 

All of the plugs were pretty gapped/burnt. I'm almost thinking the plugs were never changed in that car and it has over 130k miles on it. The back two plugs (cylinders 3 and 5) also had oil on the coil packs and a little on the plugs as well. I've already looked into ordering a replacement valve cover for that issue, and I'm also going to try some pouring some rear main seal repair in with my oil on the off chance that it might help stop the leaks.

 

Don't put that crap in your car; I get it's supposed to swell seals and what not, but think of what other small galleys it could also possibly affect.

How much oil was there? I had a leak in my cylinder 5 when I went to replace my valve cover gaskets. They were brittle and leaking oil everywhere, I just covered that one spark plug hole with RTV on the inside and under the cover. I haven't checked it yet, but hopefully it will save me 300 dollars for a new cover.

Changing that side of the cover was also a real PITA.

 

No. Don't use that crap. It causes the seals to swell in order to make the seal. It may fix the issue, but it may cause other issues to pop up.

Fix it right