Hi I have a EJ18 1994 Impreza non turbo.

 

I need to know where an what the o2 sensor does?

Does this affect the performance of my car?

 

thanks

have we met before!?!?!

 

If by "does it affect performance of my car" you mean "can it cause my current engine problems?" that first depends on what problems you're having, but yes it can affect performance.

 

with an old O2 sensor you'll usually have bad gas mileage, that's about it. doubt it's causing your problem...unless your problem is bad gas mileage.

I just got told that I should change the sensor now because I have done 185K

 

Where is this located and what does it look like?

it's the only part threaded into the exhaust that has a wire coming out of it, very easy to find. crawl under the car and look where the two sides of the exhaust come out of the engine (exhaust manifold/headers). where those two sides meet at a 'Y' is essentially where the O2 sensor will be.

 

depending the vehicle, some are easier to access from the engine bay, some from underneath. on your impreza i'm thinking it'll be easier from the engine bay (how i did the last impreza i did).

as a test you can try unplugging the O2 sensor to see if that gets rid of any hesitation or noticeable issues. the car should run fine (bad gas mileage) with the O2 sensor unplugged. that's an easy no-cost test you can try. it won't tell you if the O2 is giving you bad gas mileage but might tell you if it's causing noticeable drivability issues (i doubt it).

 

is the engine all stock...stock air filter, hose, etc?

Is it a silver metal wire that is plugged into the exhaust..

 

Yes my car is stock. Just a 3inch tip muffler.