does it take more than a split second for your car to actually shut off? when u pull the key out, does the engine sound like it shuts off immediately? if ur engine doesnt shut off immediately, your car could be doing something called "dieseling", which isnt good in any case. dieseling is a condition in which gasoline continues to fire after the ignition has been shut off. In late-model engines, dieseling , or run-on, is caused by heat and the unusually high manifold pressure that result from retarding the spark at idle. In fuel-injected cars when the engine is turned off, fuel is automatically shut off, eliminating dieseling. dieseling can effect your engine's performance, as well as the life of your engine. make sure that itz not doing that, or else you may need some engine work.