Engine keeps dieseling?

In this problem the car engine just never stops,it keeps on running,even though the ignition key is out and ignition is turned to OFF position.


The dieseling may be due to excess of  carbon deposits on top of the pistons.
After you turn off a hot engine, the carbon deposits continue to glow a little and ignite any unburned fuel OR the issue with fuel mixture is too rich.
Also inspect condition of  spark plugs after letting the engine get hot and running it at speed for 15-30 minutes. The plugs should not be dirty or blackened with carbon layer build-up on it.
A correct fuel mixture and proper ignition timing will leave them clean with a slight tan or grey color.
Modern engines on latest cars don't notice this Dieseling because the fuel is automatically shut off when the engine is turned off.

The other possibility can be issue anti-Dieseling solenoid.Some car engine have this solenoid,located on the throttle linkage as the idle stop.
As per its procedure,when you start the engine,the solenoid opens up and when you stop the engine the solenoid closes.But if in case this solenoid is not getting OFF,then engine will keep on dieseling and such problems will be noticed.Not all car models have this Solenoid.


This details will help.
Thanks.

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