I have a 2001 Nissan Sentra GX. I just recently had the front catalytic converter replaced but still have an exhaust (or unburnt fuel??) smell inside but ONLY when idling with the heater on. If the heater is off, or if I am driving and the heater is running - no smell.
Any ideas???
You need to bring this back…driving with the windows open…and have him look at it. You may have a leak in one of the joints from the cat converter replacement. This could be dangerous, as carbon monoxide may be getting onto the passenger cabin.
The above is sound advice. Take it back to the shop who did the cat converter replacement.
There is another possibilty, however, that is unrelated to the recent work. Have you had your oil changed lately? If so, there may have been some spillage. In that case you are smelling the remnants of the spill as it drips onto the hot exhaust system. Such a problem soon clears up by itself.
But check into the first possibilty. Do it ASAP.
When the heater is on is the air recirculating or coming in from outside? Do you get the smell with fresh air? You should have this looked at pronto.