85 Buick Lesabre Limited sedan, 307 V8, continues to run after turning it off.?

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bobby lee

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After shutting it off, it sputters for a few secconds before letting out a big sigh and finnaly shutting up. the sound is comparable to running out of gas. What could be the cause of this and how can it be fixed?
 
its more than likely a high wear engine with carbon build up. if you have a carb, there should be an antidiesel solenoid that completely shuts off airflow, no air no diesel effect. if you dont have the original carb, then quickly depress the gas when shutting off(let it rev, turn key off,lift foot).also check vac lines and pcv valve. if your injected, i guess either try water to loosen sediment, raise timing and drive for a few miles or try miracle cure, or you could break it down and clean the combustion chamber. if you have electric fans and dont have em installed in the original wire loom, they can act as a generator and keep powering the coil, with the efficiency of the said generator, it would also duplicate those symptoms.lowering the ignition voltage until its to weak to run, if you have a good charging system, it will miss and act up but run forever or until out of gas.
 
This is a complaint I haven't heard in years - and it was a very common complaint at the time.
It's often called "dieseling" and it's caused by too high an idle speed, not allowing enough time for the idle to completely slow down before the key is shut off or a faulty idle dashpot which doesn't allow the throttle to close quickly enough.
Generally, if nothing else works, shut it off in gear and then put it in park.
 
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