When your engine runs rough - that engine, how does the exhaust smell?
If exhaust is LEAN - you don't have any true sense of unburned fuel to smell
Rough running engines exhaust usually means also a misfire - which would smell of raw or heavy odor of fuel in the fumes.
Now the issue of sensor, how is the Catalytic? Is it ok? Undamaged? Is it Doing its job of taking otherwise stinky exhaust and making it more tolerable?
The "Lean" condition can also be from EGR issues but since this thing is a 5-speed and has got over 92,000 Miles - it's more than likely a problem with the GDi-type of fuel system (which is Gas Direct Inject) where the injector is in the TOP of the cylinder - In the cylinder head.
- IT may be plugged or carboned up so the fuel spray into the cylinder is not the best vaporous mist. A combustion chamber problem.
- Have you tried a fuel system cleaner, or something called Regane? Might want to try that - or just need to run a premium fuel for a tankful and use it on highway miles above 50mph so the hotter cylinder head heat and the exhaust system can clean and clear out some of this mess
- - once that is done and the engine still runs rough - it'll need more TLC including a verify (inspect) and even a plug change - that the spark plugs are not fouling out or cracked. Haven't heard from you about those...it's getting close to their time. The plugs and their condition would show which gasket (per cylinder) is leaking or if there is even a vacuum leak or other condition causing this.
- Forgive the redundancy, the service history questions need to be asked to know how the condition came to be.
- In "Vacuum leak" issues, many focus on the intake, which yes, it does make sense, but when the attempts to locate such leaks - they can't be found - many don't realize that the PCV valve hose or the exhaust manifold can cause poor vacuum issues that are overlooked.
It's a good idea to spray around those known areas where air can get in - if it's not leaking oil or at least not burning it - it's a good sign to know it is still healthy.
Other things to check:
I might be wise to check the exhaust manifold and its condition - a small leak can turn into a major vacuum leak of air returning to the system instead of thru the exhaust pipe - leaning out an engine in itself knowing it will need to run lean during deceleration changing the way the O2 sensor registers Lean.
Another type of condition that causes this is when a lot of cleaners get used all at once on the engine - Carb Cleaner while the engine is running - another cleaner in the fuel system as an additive - and then several shots of another cleaner into the throttle body again while the engine is running - can make the Catalytic converters "honeycomb" a large pack of cement and it's due to the carbon now plugging the ports the exhaust flow needs to go thru to convert that CO to CO2 S2H4O into a lesser problem child - it can't when the catalytic is plugged with carbon.
This condition is similar - a main chokehold of older cars that oftentimes burn oil - do the same thing.
The problems are, when this part gets plugged, there are NO OTHER WAYS for the exhaust to go except thru it, or out thru a gasket that is located on the engine. This condition is called backpressure - in some instances, the engine stalls because the exhaust gases can't escape so they remain in the combustion chamber and even in the EGR valve in the automatic transmission types, is forced open by this pressure - the engine is an air pump - it can't pump if it can't push the air thru it.
Another is from the catalytic getting damaged by road debris, it can dent and crush or break the honeycomb structure that has the catalyst conversion metals that do the actual process - rendering it less effective so the system sees less of one type of fume in the exhaust, and more "raw exhaust" meaning that the O2 sensors are reading about the same value - tells the system to look for problems.
So you have two extremes of conditions that can set this code, one - the second sensor (downstream one) sends back similar data as the upstream one (catalyst ineffective or gone) or the second sensor tells the system there's more O2 and so it checks the fuel mixture and trim shows it's already at extreme ends of the scales at a particular throttle position (above idle) so it can't go beyond a range to fix this condition - again too much O2 can simply be that the exhaust system has a leak and that the air in the pipe is fresher than the exhaust should have in it - so it checks with Upstream sensor - finds its getting fresh air too - means ok - turn on the lights, I've got issues.
To see O2 sensor Bank 1 or Bank 2 (versus Bank 0) - means the system is still healthy- just the catalyst might need an inspection.
