So I own a lovely 2003 mazda protege5 and I love it do death but ever since I bought it, I've been trying to fix the problems it came with. I've had the 2 codes P0171 and P0304 for the longest time and I've had 0 luck with figuring out how to fix it. I've replaced almost everything I know that would lead up to those problems and fixing other random codes that have popped up such as the fuel pressure regulator, all my spark plugs, ignition coils. vacuum tube, vacuum solinoid, and my starter. The current symptoms of my car is that on a cold start, it sometimes wont turn over and ill get a gross sulfur/gun powder smell filling up my car, or it turns over very roughly. I also have a squeaky bearing in my accessory belt if that means anything. My car also has a constant smell of gas and my fuel meter lowers when in idle. I've kinda run out of options on what to do, I really don't want to take it into a mechanic because this car is my project and I want to be the one who fixes her. Thanks for the help guys.

 

P0304 its a misfire code so .plugs ,coils and wires need to be checked
and i think the p0171 has to do with fuel too lean or too rich and thats probably because of the misfire , oil change and coolant check woukdnt hurt ,or do a compresiion check on each cylinder ,,