Every since i got that code said random multiple cylinder misfire (90300) I've been getting really crappy MPG.. I got the PCV update...new filter and snorkel and new plugs.. I just dont know.. I bought gas tonight got about a quarter tank of gas exactly it said I had 115miles on my SID. drove literally 16miles and not the SID said i have 35 miles left and my gas light is on.;.what the hell is going on.?