Engine exhaust smell coming inside through air vents

[npm]

Hi all,

On my 1999 Pathfinder, right when I turn the ignition on with the fans or A/C on, I get a strong running engine/exhaust smell inside the car. After this, the smell goes away even when the fans are on. So it only happens at startup. Any ideas what could be causing this?

Thanks!

[rgk]

A rich condition due to the O2 sensors not being warmed up coupled with an exhaust leak at the header or manifold.