Why does the my engine sound like it is still running after I turn off the car?

Dear Car Talk

Dear Car Talk | Dec 01, 1992

Dear Tom and Ray:

I have a 1986 Ford Escort. After I turn off the ignition and pull out the key, the car still sounds like it's running. Why?

RAY: Because it is, Carlos.

TOM: When this happens, it's called "dieseling," because it's running like a diesel engine--that is--without spark plugs. When you turn off the ignition in your Escort, you're turning off the spark plugs, and when you stop sending spark to the cylinders, the car is supposed to stop running.

RAY: One thing that could cause dieseling is an engine that's running too hot. If there's something wrong with the cooling system, if the timing is too advanced, or if it's just a very hot day, the temperature inside the cylinders could be high enough to ignite gasoline even without the benefit of spark.

TOM: Another possibility is that the engine is simply running too fast. If the idle speed is set too high (which could also be caused by timing that's too advanced), the momentum of the engine could keep it running for a few seconds after you turn it off.

RAY: Have the idle speed and the operating temperature checked, Carlos. And in the meantime, just maintain a dignified look and walk away from the car quickly after you park it.

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