Hi, I bought a 04 g35 mt with a vortech v3(111,xxx) about 3 weeks ago in Tennessee.The car had a p0300(random misfire).I changed plugs on the spot because prev-owner told me he had never changed plugs and the car was sitting since 2013.He was the second owner only had it for about 2013. The old plugs were coated with oil on the tips. He had told me that he only changed the driver side valve cover. Now the check engine light was blinking than turned in a light that stayed on. Pro-demand and the factory service manual both say that the flashing mil mean the misfire can cause damage to the catalytic converter.I settle on a price and buy the car, but i tell the owner that I'll call a shipping company to move the car. Fast forward to last Thursday(9/5/19). Car arrives at my house.The car has a weird no start(crank but no start).The car had a full vortech v3 supercharger kit(this included the A-Pillar gauges).They showed my fuel pressure,water temperature and total boost.I had 50+ psi of fuel pressure so it was very odd and checking the scanner I found 2 new maf codes (p0102 and p0113).I push the car in my garage. I pull all the plugs (2 of the tips have oil on the them) I clean them and reinstall them in the engine (These are new ngks that have less then 10 miles one them)Then then engine started up, further more the p0300 disappeared. All that was left were the 2 maf codes.I cleaned the maf codes but nothing changed.So my next step is to change the maf.

Now my first question is do i need to do an ecu relearn after changing or cleaning the maf.If so will I lose my tune?And if a new maf (dealership part) doesnt fix the codes what should i check next?The harness?

Second question is the the car has had a rather aggressive rattle, kinda reminds me of a diesel engine. It had this rattle when I started it in Tennessee so this isn't new. I have a video of the rattle.The rattle doesn't sound like a a heat shield like other threads have posted but i could be wrong.Is this a valve problem or timing problem or fuel dampner or somthing else?The rattle is inaudiable at higher rpms.