New 370z owner in San Antonio, Tx

mmares94

So I just bought a 2009 370z Touring Manual. So far it has a Stillen exhaust and I just bought a K&N Cold air intake to install this week. Ive had a few issues with it since I bought it about a month ago. First of all my fuel gauge sensors are reading wrong. When Im close to empty my gauge reads half and when I should be at a half my guage reads 3/4. So I know atleast one of the two sensors is off but I don't know which one. I also don't know how to do it. Most mechanics would charge about 400$ for just service not including parts. Next my service engine soon light is on and at moments it'll blink. Ive read the code and its p0300 random cylinder misfire and just that code nothing else. In idle im sitting at about 1.2 revs which I think is a little high. I have not had the chance to change spark plugs but that is one thing im going to try next. Any ideas on the fixes? or point me towards a thread that does have the answers? Thanks for any info I might get.