Why does your car want to start when you turn it off?

The problem is called "dieseling" or "engine run-on" and happens primarily in cars with carburetor engines. It occurs when the engine is shut down because fuel in the cylinders is being ignited without a spark, but by a hot spot in the cylinder. The problem isn't as prevalent in cars after 1990, since most are now fuel-injected.

There are several things that can cause dieseling - refer to the link below to view them.