Dieseling after shut off

[87rustbucket]

So every once in a while when I shut off my car after normal running and the engine will keep running (very roughly) for a second. And when I go to start it back up after that happens it is much harder to start up. I know that this is not normal and rarely happens so I'm not worried about it but wandered what causes it and what it is an indicator of.

My car is has a carb and has nearly 300,000 miles on it.

[Griff]

From my understanding it is caused when there is high heat or pressure (pressure and heat are directly related) the heat energy required for combustion is enough to ignite the fuel. A lot of carbon build up, which will hold the heat in the cylinder, can cause this I think. Also hot burning spark plugs or low grade fuel can cause dieseling. I'm not sure of why the engine would be harder to start though. This is just from what I remember from hearing about dieseling. Please, anyone, feel free to correct me if I am mistaken on anything.

[Griff]

I bet is is just excess carbon build up. The only disadvantage is that you are losing some of the energy from the combustion when you are driving so your car will be a little slower. My '89 Accord with 180k miles and my '93 Civic with 214k miles had a decent amount of carbon build up in the cylinders which leads me to believe that your 300k mile engine is most likely the same.

[carotman]

Maybe the idle shutoff solenoid is stuck open.

It's the solenoid behind the carburettor.

[87rustbucket]

thanks for the response, I will have to take a look at the shutoff solenoid. I don't suppose there is a way to get rid of carbon buildup with out taking the engine apart?

[Dr_Snooz]

x2 on solenoid. Dieseling can also be caused by having the idle speed set too high. To get rid of carbon, put a bottle of injector cleaner in the tank and do an Italian tune up.

[2ndGenGuy]

Also vacuum leaks can cause the dieseling as well.

[Hauntd ca3]

x2 on solenoid. Dieseling can also be caused by having the idle speed set too high. To get rid of carbon, put a bottle of injector cleaner in the tank and do an Italian tune up.

x2
I perform an Italian tune up on my mums cd6 on a regular basis.

[Vader⭐️Grl]

Thanks⭐️...my 88 Honda DX occasionally has this issue.will surely try the treatment