How do you stop the engine from dieseling?

let it cool down a bit before shutting it down,and or tune up. check timing

Your engine may be running too rich. Has your gas mileage gone down?

try using higher octane fuel

There is now straight forward answer for this question, ignition timing,fuel mixture,valve timing,computer prom,and many other factores can contribute to dieseling. A Tech would need more info. to properly diagnose the problem. For example, mileage,type of fuel & ignition system,. I will say that most dieseling can be contributed to poor octane of fuel or timing.

I had the same problem on my old truck. When you shut the engine off it starts dieseling.Check the carburetor and see if the bottom butterflies are shutting all the way, if not try adjusting it or find out why they are not shutting . This is the most common cause of your problem.