I GOT CODE SAYS IM BURNUNG RICH I HEAR A HISSING SOUND UNDER THE ENGINE COVER but can find leak or if this is the normal sound don't remember, had code cleared and has not returned in 2 months 2,000 miles
but milage is 15 mpg was 18 mpg highway to sc was 23 mpg.

 

If it's doing that it's probably damaging the cats so take to a shop and have it fixed.

 

You should probably check your hoses but if it was me I'll check the vaccum line (located on the right side of the engine if you stand in front of your vehicule) it's like a plastic hoses.

 

same problem I know this is a old thread but my car threw a cat code and I know my car is louder than before anyone have tips on how to find the leak

 

An old trick I've used is a spray bottle filled with water, start the engine and mist the engine in the area you think the vacuum leak is, the engine should stumble when you get close to, or spray into the leak. In addition, you may have to wiggle some vacuum lines to find it.

 

If your car sound different it might really be an exhaust probleme. Maybe there is a small whole in it. If it run fine on idle and there is no fluctuation in rmp it's not the engine. Check the exausth line for any whole. What is the code exactly ?