2000 Altima - Engine keeps running

Hello.

On a 2000 Altima, the engine keeps running for a few seconds after the key is turned to the 'off ' position and removed from the ignition switch. Could it be a relay?

Thanks.

It sounds like the engine is 'dieseling', are you sure you have the correct spark plugs installed? Is the tail pipe covered in black soot as if it has been running rich?

This was a false alarm. I tried to diagnose this problem from speaking to the owner. As soon as I saw the car I knew there was no problem. It was the cooling fan running after the engine was shut off. The owner usually takes short rides and usually did not even get the car up to operating temperature. Thanks anyway.