got to agree with vcv try switching brands as some have a higher sulphur % causing the smell before calling the cat dead. Army has a point but as usual always the worst possibility one first.
Kyle i will explain this as simple as possible about the intake and gas
short ram crap --this is garbage because it only ingest hot engine air which is expanded reducing the number of oxygen particles ,it sounds great has lost of power when the engine is cold after time this hot air mixed with gas creates larger deposits of carbon than normal
cold air intake where the filter is located outside the engien bay, works wonders when made properly not half assed, by receiving colder air which is more dense in oxygen to facilitate combustion and reduced intake load for vacume in an oem intake system it increases horsepower. A real basic calculation of reduced intertia of the engine used to ingest air can be used for the wheels to spin.
You are now increasing the oxygen which also needs more fuel to support the combustion properly to keep it balanced at stocih as needed.
If you use normal gas you run lean as it all gets burnt easily and causes the spent gases to get hotter than normal ,as is a lean condition.
So higher octane is mandatory for any increase in factory ecu map cruves.
By the same token an intake reduces the amount of fuel needed as it can run leaner and richer as thei is more flexability to the mapping now.
hope you understand this.