Was A/C on? I have a car (not a caddy) that used to do this only when I stopped engine with A/C compressor on. I´ve also seen cars doing that for not using spark plugs with the correct power specifications. Are you using AC R46N type?.
Usually
Advanced timing on a hot motor.
The engine will continue the combustion cycle free of ignition until the cylinders cool down enough to stop.
Thus the term dieseling.
Sometimes it can happen when the fuel in the carb boils.
As other poster pointed out.
When the A/C is on there is a dash pot that raises the idle to compensate. Some times they will continue to run for a moment after turned off.
They term this Run On.
Those are three off the top of my head?
On the side of the carburettor are vacuum brakes. When the engine is turned off they slam the throttle valve shut to cut off the air to the cylinders. When you turn the ignition off, the carburettor continues dripping fuel into the intake, so if the throttle doesn't shut completely or fast enough, it allows enough of an air/fuel mixture to keep the engine running for a few more revolutions. If there is a vacuum leak in the lines to the vacuum brakes, they won't work correctly.
I was going to suggest something that you already explained, on my 80 cdv. I was also getting dieseling, I found an old style mechanic who went right to the
small spring on side of carb., and replaced with a different return spring and the problem was solved, the old spring was not pulling back enough on the throttle to
stop the gas flow, maybe yours is the same, start simple.
Dieseling shouldn't happen on a cold engine because there is no ignition source.
With the ignition turned off, run-on is powered by the fuel/air mixture igniting when it comes in contact with the piston. Usually there are carbon deposits on the cylinders that glow red hot, that ignite the mixture. These carbon deposits can also cause precognition, because they will ignite the mixture before the spark plug (when the engine is running).
nice, thanks for the info Sven. Dieseling has happened before on my 87 due to vacuum leak and also happens now on my 69, which I'm guessing is due to timing being off due to the distributor being rusted in place.
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