First off when is the last time you've changed the fuel filter bec they should be changed yrly.
Could be many different causes and it might be as simple as changing the gas filter, checking the air filter , checking or replacing the PCV valve , plus a basic charging system overhaul , basic tune up of plugs and wires.
I'd start with the gas filter , the air filter ,change the PCV valve , gas pressure valve, cleaning the battery , starter , alternator posts and connections , the engine block ground , all grounds with a wire brush and fine sandpaper, check , clean , re-gap the plugs or replace , check clean the spark plug wire connectors inside their ends with a flat screwdriver, clean the ignition coil connections.Plus check for any codes stored in the main comp, maybe have a free scan done or check them via your ignition, plus check the O2 sensor connections and if the smell still exists I bet a o2 sensor is gone.
Hope that helps and best of luck.By the way other things can cause those sort of problems but I'd start with these basics first especially if these things haven't been done in some time.